Drizzle olive oil into a large heavy-based pot over MEDIUM heat. Add the onion, celery, carrots, mushrooms, garlic, and ground turkey. Cook for 8–10 minutes, stirring occasionally until the turkey is white and the onions are translucent.
Add the smoked paprika, coriander, oregano, crushed tomato, fresh basil, salt, and pepper to the pot. Stir well. Cover the pot. Bring to a boil then turn down the heat and let it simmer for 25–30 minutes, until the watery liquid has cooked away and you are left with a nice thick sauce. Stir occasionally to prevent the sauce from sticking to the bottom of the pot.
While the sauce cooks, make the cheese sauce by whisking the ricotta, Parmesan, egg, and nutmeg together until smooth.
Preheat the oven to 400°F. Cover the bottom of a 9 x 13-inch lasagna casserole dish with a thin layer of the turkey sauce. Layer on the lasagna sheets, then the ricotta cheese sauce. Repeat this three times until you have 3 sets of layers. Top it all off with the mozzarella slices and the rest of the Parmesan and bake in the oven for 30 minutes. Top with fresh basil.