Fish Casserole

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A super easy gluten free baked Fish Casserole recipe which combines creamy mashed potatoes, lean fish, and quick-cooking veggies into this classic comfort food.

Suitable for people following a gluten free diet. Post includes Weight Watchers points.

 

gluten free fish casserole with a serving spoon

Seafood freezer meals are the epitome of comfort food, and this creamy baked fish casserole is a classic dish perfect for Sunday lunches with the family, a filling summer lunch, easy weeknight suppers, and special occasions such as Easter, Christmas, and Father’s Day.

Nothing says comfort food better than a big old helping of homemade Gluten Free Baked Fish Casserole. This simple dish can be made ahead of time and is beyond very easy to whip up into the most creamy, filling and decadent homemade Fish Casserole recipe.

Serve it with Smashed Brussels Sprouts, Smothered Green Beans, or any of your favorite side dishes for a satisfying meal that everyone will love.

finished gluten free fish casserole ready to be served

What makes this fish potato casserole stand out is that it’s also gluten free. This recipe uses cornstarch (cornflour) instead of flour to make the roux that thickens up the casserole sauce.

And, I have also used a variety of fish to complete this Healthy Seafood Casserole, rather than just sticking to one fish or the other. This is one of those ‘the more the merrier’ kinda recipes.

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Why Make This Baked Fish Casserole Recipe

  • It’s flavorful and adaptable. Fish can be seasoned and flavored in various ways, making it adaptable to different taste preferences and cuisines.
  • It’s comforting. Seafood freezer meals and casseroles often have a comforting, homey appeal, making them perfect for cozy dinners. It’s an easy meal that will be a family favorite.
  • It’s healthy. Fish is a lean source of protein and is rich in essential nutrients like omega-3 fatty acids, which are beneficial for heart and brain health.

Making casseroles is a great way to save time and money. Check out these casseroles for more flavorful ideas your family will love. 

Ingredient Notes

  • Potatoes – Use your favorite potatoes to make mashed potatoes as a topping for the casserole. You can use different types of potatoes like russet, Yukon Gold, or red potatoes. Sweet potatoes could also be used for a unique twist.
  • Butter – I opt to use dairy-free butter, but you can use regular butter if you’re not following a dairy-free diet. Alternatively, use coconut oil or olive oil for a dairy-free option.
  • Plant-based milk – Plant-based milk is used to make the mashed potatoes creamy and as a part of the casserole sauce. Any type of plant-based milk like almond, soy, oat, or cashew milk can be used. Regular dairy milk is an option if you’re not going dairy-free.
  • Olive oil – Use your favorite light, neutral flavored cooking oil, such as extra virgin olive oil.
  • Green Onions – Green onions add a mild onion flavor to the casserole. You can use regular onions or chives as a substitute for green onions.
  • Cornstarch – Cornstarch is used as a thickening agent for the casserole sauce. You can substitute arrowroot starch or potato starch for cornstarch if desired.
  • Dijon Mustard – Dijon mustard adds a tangy flavor to the casserole sauce. You can use yellow mustard or whole-grain mustard as a substitute.
  • Ground Nutmeg – Nutmeg adds a warm, aromatic flavor to the sauce.
  • Anchovy Fillets – Anchovy fillets provide a savory, umami depth of flavor to the casserole. If you don’t like anchovies, you can omit them or use a vegan fish sauce substitute.
  • Fish Pie Mix – Fish pie mix typically includes a variety of seafood such as white fish, salmon, and smoked fish. You can use a mixture of your favorite seafood like cod, salmon, shrimp, or any other fish you prefer. You can also use fish fillets that have been cut into bite-sized pieces.
  • Baby Spinach – Baby spinach adds a fresh and vibrant element to the casserole. You can use other leafy greens like kale or Swiss chard if preferred.
  • Frozen Peas – Peas provide sweetness and color to the casserole. Fresh peas or canned peas can be used instead of frozen peas.

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How To Make Fish Casserole

Get complete ingredients list and instructions from the recipe card further below.

  1. Boil and mash the potatoes with some plant-based milk and dairy-free butter, then set aside.
  2. Melt butter in saucepan, add in and sauté green onions before adding cornstarch.
  3. Slowly whisk in the plant-based milk, then bring to a rolling simmer, stirring continuously until the sauce is thick.
  4. Switch off the heat, then stir in mustard, nutmeg, anchovies, fish casserole mix, baby spinach, and peas before transferring to a prepared casserole dish or baking dish.
  5. Top with mashed potatoes and bake for 25 minutes in the hot oven until golden and the mixture is bubbling.
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Pro Tips

  • If you are starting with whole fish, then make sure to cut into similar-sized chunks so they cook at the same time.
  • If you have less fish than the recipe calls for, you can bulk up your fish casserole with extra veggies.
  • Choose fresh fish, vegetables, and herbs to ensure the best flavor and texture in your casserole.
  • Season each layer with salt, pepper, and any desired herbs or spices to enhance the overall flavor.
  • Ensure you’re using an appropriately sized casserole dish. It should be large enough to comfortably fit all the ingredients without overflowing.
  • Always preheat the oven to the specified temperature in the recipe to ensure even cooking.
  • You want the casserole to be a nice golden brown. If the casserole tends to brown too quickly on top, cover it with aluminum foil for part of the baking time to prevent excessive browning.
  • Allow the baked fish casserole to rest for a few minutes after removing it from the oven. This helps the flavors meld together, and it will be easier to slice and serve.
  • Baked casseroles are best served hot, so try to time your meal to be ready when the fish casserole comes out of the oven.
  • Add a squeeze of fresh lemon juice.
gluten free fish casserole with a serving spoon

Recipe Variations

  • Swap the veggies. Feel free to add more quick-cooking vegetables like green beans and sweetcorn.
  • Add shrimp. You can also add shrimp to the chopped fish mix.
  • Swap the potatoes. Try using mashed sweet potatoes instead of regular mashed potatoes.
  • Add fresh herbs. Fresh herbs like parsley, dill, or chives can be added at the end for a burst of freshness and color.
  • Top with pastry. If you prefer, you can make this a fish pie with pastry. To do so, simply skip the mashed potato and cover the fish casserole mix with puff pastry and then bake. Just make sure you are using a gluten-free pastry.
  • Add cheese. If you want to upgrade this to a cheesy seafood casserole you can. Simply take the casserole out after about 15 minutes and top with lots and lots and lots of cheese. Then return to the oven until cook time is done. Parmesan cheese is a tasty choice but you can also use cheddar cheese.

Prep and Storage

  • Prep – Defrost frozen fish and prep all of your ingredients.
  • Store – Leftover casserole should be stored in an airtight container in the fridge and consumed in 2-3 days.
  • Freeze – Just assemble, and instead of cooking right away, cover tightly and freeze. If you are going to freeze it, then start with fresh fish rather than frozen fish. A perfect make-ahead meal prep solution!
  • Reheat – Preheat the over to 275 degrees F / 140 degrees C. Add a splash of milk or water to the casserole and cover with foil. Reheat for about 12-15 minutes till warmed through.
top down view of gluten free fish casserole with a scoop removed

FAQs

What type of fish to use for fish casserole?

You can use your favorite type of fish for this baked casserole. You can also buy whole fish and then chop it into suitable-sized pieces. However, the easiest thing to do is go to your local market and buy some fish pie mix, which comes with a nice variety of fish.

Can I make this with frozen fish?

Frozen fish is convenient and affordable and you can make this with frozen fish. However, the fish should be thawed completely before assembling and baking the casserole.

How do I prevent fish from becoming dry?

To prevent overcooking and dry fish, follow the cooking times accordingly.

Can I bake this later?

Yes, you can prepare the casserole in advance and refrigerate it until you’re ready to bake it. Just be sure to increase the baking time slightly if the casserole is cold from the refrigerator.

More Gluten Free Fish Recipes

Want more gluten-free fish recipes? Then try these tasty dishes:

Serve With:

This baked fish casserole makes a great meal by itself but if you want to stretch it out a little bit, then feel free to serve any of  these sides:

Weight Watchers Points

There are 7 Blue Plan SmartPoints in one serving of this.

More Casseroles Recipes

Be sure to try some of my other awesome casserole recipes!

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A fish pie with some scooped out with spoon and some fish on a table
Print Recipe
4.91 from 10 votes

Fish Casserole

This simple dish can be made ahead of time and is beyond very easy to whip up into the most creamy, filling and decadent homemade Fish Casserole.
Prep Time5 minutes
Cook Time40 minutes
Total Time45 minutes
Course: Main Course
Cuisine: American, Western
Diet: Gluten Free
Servings: 6
Calories: 287kcal
Author: Bintu Hardy

Ingredients

  • 2 pounds (1kg) potatoes, peeled and cut chunks
  • 4 tablespoons dairy-free butter divided
  • 2 cups (500ml) plant-based milk use ¼ cup for mashed potatoes; 1 ¾ cups for casserole.
  • 2 teaspoons olive oil
  • 2 green onions finely sliced
  • 4 teaspoons (20g) cornstarch
  • 1 teaspoon Dijon mustard
  • ½ teaspoon ground nutmeg
  • 4 anchovy fillets finely chopped
  • 1 ½ cups (400g) fish pie mix
  • 2 ½ cups (75g) baby spinach roughly chopped
  • ½ cup (75g) frozen peas

Instructions

  • Preheat the oven to 400 degrees F / 200 degrees C.
  • Add the potatoes into some salted boiling water, bring back to the boil, reduce to a simmer cook until tender.
  • When done, drain, let cool for a few mins and mash with a 4 tablespoons of milk and 2 tablespoons of dairy-free butter and set aside.
  • Melt butter in a sauce pan, add green onions and cook for a minute, then add in cornstarch and cook for a minute.
  • Slowly whisk in the milk, then bring to a rolling simmer while stirring continuously (to avoid any lumps) for 3 – 4 minutes until the sauce is thick.
  • Switch off the heat, then stir in mustard, nutmeg, anchovies, fish pie mix, baby spinach and peas before transferring mix to a baking dish.
  • Top with the mashed potatoes and bake for 25 minutes in the hot oven until golden and the mixture is bubbling.
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Notes

    • If you are starting with whole fish, then make sure to cut them into similar-sized chunks so they cook at the same time.
    • If you have less fish than the recipe calls for, you can bulk up your fish casserole with extra veggies.
    • Choose fresh fish, vegetables, and herbs to ensure the best flavor and texture in your casserole.
    • Season each layer with salt, pepper, and any desired herbs or spices to enhance the overall flavor.
    • Ensure you’re using an appropriately sized casserole dish. It should be large enough to comfortably fit all the ingredients without overflowing.
    • Always preheat your oven to the specified temperature in the recipe to ensure even cooking.
    • If the casserole tends to brown too quickly on top, cover it with aluminum foil for part of the baking time to prevent excessive browning.
    • Allow the baked fish casserole to rest for a few minutes after removing it from the oven. This helps the flavors meld together, and it will be easier to slice and serve.
    • Baked casseroles are best served hot, so try to time your meal to be ready when the fish casserole comes out of the oven.
    • There are 7 WW Blue Plan SmartPoints in one serving of this.
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Nutrition

Calories: 287kcal | Carbohydrates: 31g | Protein: 17g | Fat: 11g | Saturated Fat: 2g | Polyunsaturated Fat: 3g | Monounsaturated Fat: 5g | Trans Fat: 1g | Cholesterol: 31mg | Sodium: 232mg | Potassium: 939mg | Fiber: 5g | Sugar: 2g | Vitamin A: 1310IU | Vitamin C: 39mg | Calcium: 147mg | Iron: 2mg

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