Heat oven to 375. Coat a 13x9-inch pan with cooking spray.
Heat oil in a large nonstick skillet over medium-high heat. Add onion and cook for 5 minutes until lightly browned. Add tomatoes, beans, corn, chili powder, salt and garlic powder to onions. Bring to a boil and simmer for 10 minutes until mixture is slightly thickened; set aside.
Spread 1/4 cup enchilada sauce on bottom of baking dish. Tear up 8 of the tortillas and layer over sauce. Spoon on bean mixture. Pour 1/2 cup enchilada sauce evenly over bean layer.
Tear up remaining 8 tortillas and layer over sauce. Pour remaining sauce over top and sprinkle with cheese. Bake for 25 minutes or until bubbly and cheese is melted.