Heat a large skillet over medium heat. Add the ground beef, chopped onion, and minced garlic. Cook until the beef is browned and the onion is soft. Drain any excess fat.
Stir in the drained kidney beans, diced tomatoes, chili powder, cumin, and salt. Let the mixture simmer for 10 minutes so the flavors combine.
While the chili simmers, combine the cornmeal, flour, and baking powder in a mixing bowl. Add the milk, egg, and vegetable oil. Stir until a thick batter forms.
Pour the chili into an oven-safe baking dish. Spread the cornbread batter evenly over the top.
Sprinkle the shredded cheddar cheese over the batter. Bake at 400°F for 20 minutes until the topping is golden and set.