Preheat your oven to 350°F (175°C) to prepare for baking your casserole.
In a large skillet over medium heat, add the lean ground turkey. Cook it until it‘s browned and fully cooked through, breaking it up with a spatula as it cooks.
Once the turkey is cooked, add the finely chopped onion to the skillet. Sauté until the onion is translucent and fragrant, about 3-5 minutes.
Stir in the cumin, cayenne pepper, black pepper, sea salt, and salsa. Mix everything well and let it simmer for about 5 minutes to allow the flavors to meld.
In a baking dish, layer half of the cut whole-wheat tortillas at the bottom. Pour half of the turkey mixture over the tortillas, then sprinkle half of the reduced-fat cheddar cheese. Repeat the layers, finishing with the remaining cheese on top.
Place your casserole in the preheated oven and bake for about 25-30 minutes, or until the cheese is melted and bubbly.
Once done, remove the casserole from the oven and let it cool for a few minutes. Top with diced avocado and fresh tomato if desired, then serve warm.