Preheat oven to 375°F (190°C). Grease a 9x13 baking dish or a cast-iron skillet.

Cook ground beef with chopped onion and bell pepper over medium-high heat until browned and vegetables are soft, 6–8 minutes. Drain excess fat if necessary. Stir in garlic, chili powder, cumin, salt, and pepper; cook 30 seconds.

Remove from heat and stir in drained whole-kernel corn, creamed corn, diced green chiles, and half of the cheddar cheese.

In a separate bowl, whisk together cornmeal or muffin mix, milk, egg, and melted butter until just combined.

Spread the beef-and-corn mixture in the prepared dish. Pour cornbread batter over it and smooth gently. Sprinkle remaining cheddar on top. Bake 30–35 minutes until golden and a toothpick comes out mostly clean.

Let the casserole rest 5–10 minutes before scooping. Serve with sour cream, cilantro, or extra jalapeños if desired.