Preheat oven to 400°F (200°C).
In a skillet over medium heat, cook ground beef and diced onion until browned. Drain any excess fat.
Add garlic, tomatoes, chili powder, salt, and pepper. Stir and simmer for 2–3 minutes. Remove from heat and stir in shredded cheese.
In a bowl, combine cornbread mix, milk, and egg. Stir until just mixed, then fold in cheese and corn.
Spread beef mixture in a greased 9x9-inch baking dish. Pour cornbread batter over the top and smooth gently.
Bake for 18–22 minutes, or until the cornbread is golden and cooked through.
Let rest for 5 minutes before serving. Enjoy!