Preheat your oven to 400°F (200°C). Grease a 9x13 inch baking dish.

In a large skillet, cook the ground beef over medium heat until browned. Drain any excess fat.

Add the diced onion to the skillet and cook until softened, about 3-4 minutes.

Stir in the cooked rice, diced tomatoes with green chilies, corn, and taco seasoning. Mix well to combine and heat through.

Pour the beef and rice mixture into the prepared baking dish and spread out evenly.

In a medium bowl, combine the cornbread mix, milk, and egg. Stir until just combined.

Pour the cornbread batter over the beef and rice mixture, spreading it out evenly.

Sprinkle the shredded cheddar cheese over the top.

Bake in the preheated oven for 20-25 minutes, or until the cornbread is golden brown and cooked through.

Let it cool for a few minutes before serving. Enjoy this comforting and flavorful casserole!