Prepare the oven and pan: Preheat oven to 350°F. Lightly grease an 8-by-11 or 2-quart baking dish.
Cook the filling: In a large skillet, heat oil over medium heat. Add the chopped onion and bell pepper and cook for 4 to 5 minutes until softened. Add ground beef and cook until browned, breaking it up as it cooks. Drain any excess fat.
Season and combine: Stir in chili powder, garlic powder, salt, pepper, enchilada sauce, and refried beans. Cook for another 2 to 3 minutes until heated through and well blended. Remove from heat.
Layer the casserole: Spread a thin layer of the beef mixture in the bottom of the dish. Layer 4 tortillas (tearing to fit as needed), half of the beef mixture, and 1/2 of the cheese. Repeat with 4 more tortillas, the rest of the beef mixture, and the remaining cheese. Sprinkle olives on top if using.
Bake: Transfer the casserole to the oven and bake (uncovered) for 25 to 30 minutes, until hot and bubbly. Let it rest for 10 minutes before serving with your favorite toppings.
Notes
How to Warm Corn TortillasTo prevent cracking and make layering easier, warm the tortillas before using:
Microwave: Wrap the stack in a damp paper towel and microwave for 30–45 seconds.
Oven: Wrap in foil and heat at 350°F for 10 minutes.