In a large skillet, brown the ground beef with the chopped onion over medium-high heat. Drain off any excess grease.
Stir in the refried beans, enchilada sauce, diced green chilies, chili powder, cumin, salt, and pepper. Cook for 5 minutes, stirring occasionally, until heated through.
Spread half of the meat mixture evenly in the bottom of a 9×13 inch baking dish.
Arrange half of the tortilla quarters over the meat mixture.
Sprinkle half of the shredded cheddar and Monterey Jack cheeses over the tortillas.
Repeat the layers: spread the remaining meat mixture, top with the remaining tortilla quarters, and finish with the remaining cheeses.
Bake for 20-25 minutes, or until the casserole is bubbly and the cheese is melted and lightly golden.
Let stand for 5-10 minutes before serving. Serve with your favorite toppings.
Notes
For a spicier casserole, add a pinch of cayenne pepper to the meat mixture.
If you don’t have corn tortillas, flour tortillas can be used, but they may become softer.
This casserole freezes well. Let it cool completely, then cover tightly and freeze for up to 3 months. Reheat in the oven or microwave.