Preheat the oven to 375 degrees and grease a 9 by 13 inch baking dish.
In a large pot, saute the onion in the olive oil until translucent. Add the bell pepper, garlic, chili powder, salt, and pepper to the pot, and sauté for 3 minutes, or until the pepper are tender.
Add the enchilada sauce, black beans, pinto beans, corn, and cilantro to the pot. Bring to a simmer briefly.
To make the casserole, place 5 tortillas in the bottom of the baking dish. Place half the bean mixture on top, and sprinkle half the cheese on top of that. Then make a second layer, starting with tortillas, then bean filling, then the remaining cheese on top.
Bake covered with foil for 15 minutes. Then remove the foil and cook for an additional 5, or until the cheese is fully melted.
Serve warm, garnished with your favorite enchilada toppings.