Chicken Enchilada Casserole

1 lb chicken, cut into small pieces, or 1 can chicken 12 oz
1 small onion, chopped
2 TBS olive oil
2 ( 10 3/4 oz) cans cream of chicken soup
1 cup sour cream
1 (4 0z) can diced green chilies
2 cup grated Colby jack or Cheddar cheese
1 (15 oz) package flour tortillas

Saute onion with olive oil in large frying pan over medium heat. Add chicken pieces and cook thoroughly. Stir in soup, sour cream and chilies. Stack tortillas and cut, with a sharp knife, into thin strips. In a greased 9" x 13" glass baking pan, layer half of shredded tortillas, half of chicken mixture, and half of chese; repeat. Bake for 30 minutes at 350 degrees.