Preheat the oven: Preheat the oven to 375°F (190°C). Lightly coat a 9 x 13-inch (23 x 33 cm) baking dish with nonstick cooking spray.

Cook the vegetables: Heat the olive oil in a 12-inch skillet over medium heat. Add the diced onion and bell pepper. Cook for 4 to 5 minutes, stirring occasionally, until the onion becomes translucent and the pepper begins to soften.

Brown the ground beef: Add the ground beef to the skillet. Cook for 6 to 8 minutes, breaking it into small crumbles, until no pink remains and the beef reaches 160°F (71°C).

Drain excess fat: If a noticeable amount of grease remains in the skillet, carefully drain it before continuing. Leaving too much fat can make the finished casserole oily.

Season the filling: Return the skillet to medium heat. Add the garlic, taco seasoning, and salt. Cook for 30 seconds, stirring constantly, until fragrant and evenly distributed.

Add the beans, corn, and tomatoes: Stir in the black beans, frozen corn, and undrained diced tomatoes with green chiles. Cook for 3 to 4 minutes, until the corn is hot and the mixture looks moist but not watery.

Add the first layer of sauce: Spread 1/2 cup (120 ml) of the enchilada sauce evenly across the bottom of the prepared baking dish.

Create the first tortilla layer: Arrange 4 tortillas over the sauce, overlapping and trimming them as needed to cover most of the dish. Small gaps are acceptable.

Add the first filling layer: Spread half of the beef mixture evenly over the tortillas. Spoon 1/2 cup (120 ml) enchilada sauce over the filling, then sprinkle with 1 cup (115 g) of the shredded cheese.

Repeat the layers: Arrange the remaining 4 tortillas over the cheese. Top with the remaining beef mixture and another 1/2 cup (120 ml) enchilada sauce.

Finish with cheese: Sprinkle the remaining 2 cups (225 g) shredded cheese evenly over the casserole. Drizzle the final 1/2 cup (120 ml) enchilada sauce lightly across the top.

Bake covered: Cover the baking dish loosely with aluminum foil. Bake for 20 minutes, until the casserole is hot through the center and the sauce is bubbling around the edges.

Brown the top: Remove the foil and bake for another 8 to 10 minutes. The cheese should be fully melted with a few golden spots.

Check the center: Insert an instant-read thermometer into the middle of the casserole. The center should reach at least 165°F (74°C).

Rest before serving: Remove the casserole from the oven and let it rest uncovered for 10 minutes. The bubbling should subside, and the layers should become easier to portion.

Garnish and serve: Cut or scoop the casserole into eight portions. Serve with sour cream, diced avocado, green onions, cilantro, and lime wedges as desired.