Set the oven to 350°F (175°C) and allow it to preheat. Lightly coat a 9 × 13-inch baking dish with cooking spray and reserve it for assembly.

Warm the olive oil in a large skillet over medium heat. Add the diced yellow onion along with ½ teaspoon kosher salt and sauté for approximately 5 minutes, or until the onion becomes translucent.

Stir the chili powder and ground cumin into the softened onion. Cook the spices for about 30 seconds to release their aroma.

Sprinkle in the all-purpose flour and stir thoroughly until it is evenly incorporated.

Gradually whisk in the chicken broth. Follow with the tomato sauce and freshly minced garlic, stirring until the mixture is well combined.

Bring the sauce to a gentle simmer and continue cooking for 5 minutes, stirring from time to time. For a completely smooth consistency, the finished enchilada sauce may optionally be blended.

While the onion for the sauce is cooking, place the ground beef in a separate skillet. Break the meat into crumbles and season it with ½ teaspoon salt and ¼ teaspoon black pepper.

Add the second diced yellow onion to the beef. Continue cooking for about 5 minutes, or until the beef is fully cooked and the onion has softened.

Remove the skillet from the heat and carefully drain away the excess fat. Fold in the drained black beans and diced green chiles.

Measure ½ cup of the prepared enchilada sauce into the beef mixture and stir until the filling is evenly coated.

Spread ½ cup of enchilada sauce across the bottom of the prepared baking dish.

Coat 6 corn tortillas in the remaining enchilada sauce, then arrange them across the bottom of the dish to create the first tortilla layer.

Divide the beef filling into two equal portions. Spread one half evenly over the tortillas, then scatter 1 cup of shredded Colby Jack cheese over the beef.

Dip the remaining 6 tortillas into the enchilada sauce and arrange them over the cheese layer.

Spread the remaining beef mixture over the second tortilla layer. Finish by distributing the remaining 2 cups of Colby Jack cheese evenly across the top.

Place the casserole in the preheated oven and bake uncovered for 20 minutes, or until the cheese is fully melted, bubbling, and lightly golden.

Remove the baking dish from the oven and allow the casserole to cool briefly before portioning and serving.