Preheat the oven to 375 degrees F (190 degrees C).

Heat a large skillet over medium heat. Add olive oil, then add onions. Sauté until onions just start to soften, 2 to 3 minutes. Add bell pepper; sauté 1 to 2 minutes. Add garlic and sauté until fragrant, about 1 minute.

Add ground beef; cook, breaking up beef with a spatula, until browned and crumbly, about 10 minutes. Drain any grease. Stir in chili beans. Season with salt, black pepper, and cumin. Stir in 1 cup enchilada sauce, reduce heat to medium-low, and simmer, uncovered, for 5 minutes.

Meanwhile, spread remaining enchilada sauce evenly in the bottom of a 10x8-inch baking dish.

Using a sharp knife, carefully cut a straight edge off one side of the tortillas. Place 4 tortillas with the cut edge facing the sides of the dish.

Spread half of the beef mixture over tortillas and top with 3 ounces cheese. Add another layer of tortillas, then beef mixture and 3 ounces cheese to create the second layer. Repeat layers ending with remaining cheese. Cover with foil.

Bake in the preheated oven for 15 minutes. Remove foil; bake until cheese is lightly browned, 5 to 10 minutes more. Remove from the oven; allow to rest for 5 to 10 minutes before serving. Garnish with sour cream and chopped cilantro if desired.