Preheat oven to 375°F. Cook chicken in microwave for 8-10 minutes until done. Drain off most of the liquid. In a saucepan saute onion. Add soup, salsa, chilies, sour cream and chili powder. Mix half of the soup mixture to the chicken.
Spoon chicken mixture onto flour tortillas, Line enchiladas in a 9x13 glass dish sprayed with non-stick cooking spray. Pour remaining soup mixture on top of the enchiladas, cover with foil.
Bake for 30 minutes. Remove foil, cover enchiladas with cheese and bake 10 minutes or until cheese is melted.