Start by preheating your oven to 375°F (190°C). Grease a 9x13-inch baking dish or casserole dish with cooking spray or butter.

Heat a little oil in a large skillet over medium heat. Add the ground beef and cook, breaking it apart with a spoon, until browned. Drain any excess fat.

Stir in the taco seasoning and chopped onion. Cook for 2-3 minutes until the onion is soft and fragrant.

Add the diced green chiles, corn, and kidney beans to the skillet. Stir everything together and cook for another 2-3 minutes, allowing the flavors to meld.

In a mixing bowl, combine the cornbread mix, egg, and milk. Stir until just combined; don't overmix. The batter will be a little lumpy, and that's perfectly fine.

Spoon the beef and veggie mixture into the prepared baking dish, spreading it evenly. Pour the cornbread batter over the top, spreading it out gently to cover the filling completely.

Bake in the preheated oven for 30-35 minutes, or until the cornbread is golden brown and a toothpick inserted into the centre comes out clean.

Let the casserole sit for about 5 minutes before serving. Garnish with fresh cilantro or a dollop of sour cream if desired. Serve it hot and enjoy!