In a bowl, make a paste with the olive oil, smoked paprika, cumin, oregano, garlic puree, chipotle paste (if usinlime juice, salt and pepper.
Add the lamb and toss to coat all the pieces, and allow to marinate for 30 mins or more. But if you're short on time, go ahead and cook the lamb straight away.
Preheat outdoor grill or barbecue with a flat plate to medium. One hot, spray the plate and then add the lamb.
Cover with inverted pan or a dome-shaped lid so that gets heat from all round and cooks better.
Cook covered lamb for 5-7 mins, then uncover, turn and cook for another 3-5 mins. Total cook time will be 8-12 mins, depending on the size of your cubes and how hot your grill is.
Remove lamb from grill and serve with tortillas and taco toppings of your choice.