Brown the ground beef in a large pot over medium heat, breaking it up with a spoon until no pink remains. Drain excess fat if needed.
Add the diced onion, minced garlic, and bell pepper to the pot. Cook for 5 minutes until the vegetables soften.
Stir in the diced tomatoes, kidney beans, chili powder, cumin, beef broth, salt, and black pepper. Bring the mixture to a simmer and cook for 15 minutes, stirring occasionally, until the chili thickens.
Preheat the oven to 400°F. In a mixing bowl, combine the cornmeal, flour, and baking powder. Whisk in the milk, egg, and melted butter until a smooth batter forms.
Pour the chili into a greased 8x8-inch baking dish. Spoon the cornbread batter evenly over the top, spreading it gently to cover the surface.
Bake for 20 minutes until the cornbread topping is golden and a toothpick inserted in the center comes out clean. Let the dish rest for 5 minutes before serving.