Mix ricotta cheese, feta cheese and mozzarella cheese together. Add seasoning. Set aside.
In a baking dish, lay part of the chicken pieces in dish, then top each piece with the cheese filling and spinach. Lay the other part of chicken pieces on top (like a sandwich).
Top with marinara sauce. Then sprinkle mozzarella cheese (and optional Parmesan cheese) over that.
Bake in pre-heated oven at 350 for 40-50 minutes.