Preheat the oven to 375 degrees F. Coat a 9"x13" baking dish with cooking spray.
Heat the olive oil in a large pan over medium high heat. Add the beef and cook, breaking up the meat with a spatula, for 4-5 minutes.
Add the onion and bell peppers and cook for 3-4 minutes or until softened. Add the garlic and cook for an additional 30 seconds.
Stir in the taco seasoning until the meat and onions are thoroughly coated.
Add the diced tomatoes and corn to the pan, then stir to mix everything together.
Add the can of refried beans. Stir until the mixture is thoroughly combined.
Spread a thin layer of enchilada sauce over the bottom of the baking dish.
Cut the tortillas in half, and layer 6 tortilla halves to fit in the dish. Spread 1/3 of the enchilada sauce over the tortillas, then sprinkle with 1/2 cup of cheese. Spread 1/3 of the bean and meat mixture over the cheese.
Repeat the layers, ending with layers of tortillas, enchilada sauce, and the remaining cheese.
Cover and bake for 20 minutes, then uncover and bake for an additional 20 minutes or until cheese is melted and browned.
Let sit for 5-7 minutes. Add any desired toppings, then cut into squares and serve.