Chicken Enchilada Casserole

1 small onion, chopped
2 tablespoons margarine
1 can cream of mushroom soup
1 can cream of chicken soup
1 cup sour cream
1 (4 ounce) can chopped green chiles
8 chicken breast halves, cooked and quartered
12 corn tortillas
1 1/2 cups Cheddar cheese

Saut? onion in margarine in large skillet. Stir in soups, sour cream, green chilies and chicken; set aside.

Spray a 9 x 13-inch casserole with cooking spray. Layer 1/2 of broken tortillas, chicken mixture and cheese; repeat layers. Bake at 350 degrees F for 30 minutes.