Preheat the oven to 350 degrees F / 180 degrees C and grease a 9x13 baking dish.
Heat oil in a large skillet over medium heat. Add diced onion, garlic, eggplant, bell pepper and mushrooms and cook for about 5 minutes to soften. Add the spinach and marinara sauce and stir to combine.
To assemble, spread ¼ of the tomato sauce in the bottom of the baking dish. Then place 4 lasagna sheets overlapping slightly on top of the sauce.
Spread another ¼ cup of marinara sauce on the lasagna sheets, add ⅓ of the ricotta, ⅓ of the vegan mozzarella cheese, and top with 4 more lasagna sheets.
Repeat and then finish by layering the last of the marinara sauce and ricotta cheese.
Cover with aluminum foil and bake for 50 minutes and check the noodles for doneness.
Top with the remaining vegan mozzarella cheese and broil for 5 minutes until the cheese is nicely browned.
Remove the lasagna from the oven and allow it to rest for 10 minutes before cutting and serving.
Video
Notes
You can make this with any kind of lasagna sheets. They do not need to be boiled in advance.
Layer some of the sauce on the bottom of the casserole. This ensures the noodles will cook through completely and won’t stick to the dish.
Add more veggies if you like. Almost any vegetable will work.
Add more cheese. If you love cheesy lasagna, pile on the vegan cheese.
Save time and prepare the vegetable marinara in advance, then assemble and bake.
Make the whole casserole up to 24 hours in advance and refrigerate until ready to bake.
Season to taste with salt, pepper, Italian seasoning, red pepper flakes, and more.
Use gluten free pasta to make this gluten free.
Use zucchini noodles to make this low-carb, Paleo, and Whole30 compliant.
Storage - keep in an airtight container inside the fridge for 5 days, or in the freezer for up to 3 months.