Heat oven to 400°F.

Brown beef with onions in a large nonstick skillet. Add salsa, taco seasoning, corn and beans. Mix well. Cover; simmer 5 minutes. Remove from heat.

Spray the bottom of the baking tray with cooking spray.

Cover the bottom of the baking tray with tortillas.

Cover with 1/3 of the meat mixture and 1/2 cup each type of cheese.

Add another layer of tortillas and meat and cheese. Repeat.

Cover with foil.

Bake for 30 minutes.

Uncover and bake 5 more minutes.

Optional : serve with shredded lettuce, thinly sliced radishes and sour cream.