Preheat your oven to 350°F (175°C).

Lightly spray a 9x13-inch baking dish with cooking spray.

In a large skillet, heat oil over medium heat. Sauté onions with a pinch of salt until translucent, about 5 minutes. Stir in chili powder and cumin, cooking for another 30 seconds, then add flour. Whisk in chicken stock, tomato sauce, and garlic. Simmer for about 5 minutes until thickened.

In a separate skillet, cook ground beef over medium heat, seasoning with salt and pepper. Once browned, mix in diced onions and cook until softened. Drain excess fat and stir in green chiles and black beans with ½ cup of the enchilada sauce.

Pour ½ cup of enchilada sauce into the bottom of the baking dish. Dip 6 tortillas in remaining sauce and layer in the dish. Spread half of the beef mixture, then sprinkle with 1 cup of cheese. Repeat with remaining tortillas, beef, and top with 2 cups of cheese.

Cover baking dish with foil and bake for 20 minutes. Remove foil and bake until cheese is bubbly and golden brown.

Let the casserole cool for 5–10 minutes before slicing into portions.