Preheat oven to 350°F

Chop onion

Spray casserole dish with cooking spray

Pour enough enchilada sauce into casserole dish to cover bottom

Arrange enough tortillas to cover casserole dish bottom, overlapping as necessary

Sprinkle 1/2 the cut onion onto the tortillas

Sprinkle one can of chili peppers onto the tortillas

Sprinkle 1/2 the cheese onto the tortillas

Cover with enough tortillas to cover first layer

Spread 1/2 the soup on tortillas

Sprinkle remaining onion onto the tortillas

Sprinkle remaining chili peppers onto tortillas

Sprinkle remaining cheese onto the tortillas

Cover with enough tortillas to cover second layer

Spread remaining soup on tortillas

Cover casserole dish with foil

Bake for 30 minutes in preheated oven

Remove foil

Bake an additional 5 minutes until the soup is bubbly

Serve