Preheat the oven to 375°F.

In a large skillet over medium-high heat, add the ground beef and cook for 6-8 minutes until browned, breaking it up with a spoon. Drain excess fat if desired.

Stir in the diced onion and green bell pepper and cook for 4-5 minutes until softened. Add garlic powder while sautéing.

Add the chili powder, cumin, salt, and pepper to the beef mixture. Stir in the canned diced tomatoes, drained corn, and black beans. Cook for 2-3 minutes to warm through and allow flavors to meld.

Spread the beef and vegetable mixture evenly in the skillet or pour into a greased 9x13 baking dish. Sprinkle 1/2 cup of shredded cheddar cheese over the filling.

In a bowl, whisk together the corn muffin mix, milk, and beaten eggs until just combined. The batter should be pourable but thick.

Gently spoon or pour the corn batter over the filling, smoothing it with a spatula so it covers evenly. Sprinkle the remaining 1/2 cup cheddar cheese on top if desired.

Place the casserole in the preheated oven and bake for 25-30 minutes, or until the cornbread topping is golden and a toothpick inserted in the center comes out clean.

Remove from oven and let rest for 5-10 minutes to set. Slice into squares and serve warm.