1. Preheat oven to 375° F.
2. Pour half of spaghetti sauce into a 9x9-inch casserole dish.
3. Layer pierogies over sauce and top with sliced chicken breast.
4. Pour remaining sauce over casserole and sprinkle with mozzarella and cheddar cheese.
5. Cover casserole with sprayed foil and bake for 25 to 30 minutes.
Tip: Lightly spraying the foil will keep it from sticking to the cheese.