Preheat oven to 375°F (190°C). Grease a 9x13 inch baking dish.
In a large skillet, cook ground beef over medium heat until browned. Drain off any excess grease. Add chopped onion and bell pepper and cook until softened, about 5 minutes.
1 pound ground beef
Stir in diced tomatoes (undrained) and kidney beans. Bring to a simmer and cook for 5 minutes.
1 pound ground beef
In a separate bowl, whisk together cornbread mix, milk, egg, and melted butter until just combined. Do not overmix.
1 pound ground beef
Spread the meat and bean mixture evenly in the prepared baking dish. Sprinkle shredded cheddar cheese over the top.
1 pound ground beef
Pour the cornbread batter evenly over the cheese and meat mixture.
1 pound ground beef
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean and the cornbread is golden brown.
Let stand for 5-10 minutes before serving.
Notes
This casserole is delicious served with a side salad or a dollop of sour cream.