Chicken Taco Casserole

1 package small corn tortillas
3 tablespoons butter
1 cup sliced fresh mushrooms
3 tablespoons flour
1 cup milk
1 small jar green taco sauce
1 tablespoon chili powder
2 cups cooked diced chicken
1 small can chopped green chile peppers
2 cups shredded Mexican cheese blend

Cut or tear the corn tortillas into bite-size pieces; set aside.

In a saucepan over low heat, melt butter; add mushrooms and saut