Step 1: Preheat your oven to 350°F (175°C). Gather your other ingredients while the oven warms up.

Step 2: In a large skillet, brown the ground beef with diced onion and optional bell peppers over medium heat for 7-10 minutes until no longer pink. Drain fat and set aside.

Step 3: In a mixing bowl, whisk cornbread mix, egg, and milk together until just combined. Set aside to rest.

Step 4: Spread the browned beef mixture evenly in a 9x13 inch baking dish.

Step 5: Pour the cornbread batter over the beef layer, using a spatula for an even spread.

Step 6: Bake for about 40 minutes until the top is golden brown and a toothpick inserted comes out clean.

Step 7: Allow the casserole to cool for 5-10 minutes, then slice into squares and serve.