Cut 1 cooked, boned chicken in small pieces. Cook a large finely chopped or grated onion in 1/4 pound of butter. Add chicken and 1 can green chilies. Add 2 cans chicken soup or 1 can mushroom soup and 1 chicken soup. Simmer together. Toast and crumble 1 package frozen tortillas in bottom of large baking dish (11 x 15 inch). Pour chicken mixture over this. Arrange slices of cheese on top. Bake in moderate oven until brown on top.