Step 1: Prepare the Beef and Rice Mixture

1. Heat olive oil in a large skillet over medium heat.
2. Add the chopped onion and cook until soft and translucent, about 3-4 minutes.
3. Add minced garlic and cook for another 1-2 minutes until fragrant.
4. Add the ground beef to the skillet, breaking it up with a spatula, and cook until browned, about 5-7 minutes.
5. Once browned, drain any excess fat from the skillet.
6. Stir in the cumin, smoked paprika, and chili powder, followed by the diced tomatoes and black beans. Season with salt and pepper to taste.
7. Mix in the cooked rice and thawed corn kernels. Stir until well combined and heated through. Remove from heat and set aside.

Step 2: Prepare the Cornbread Batter

1. Preheat the oven to 375°F (190°C).
2. In a mixing bowl, whisk together the cornmeal, all-purpose flour, sugar, baking powder, and salt.
3. In a separate bowl, whisk the milk, egg, and melted butter until smooth.
4. Gradually combine the wet ingredients with the dry ingredients, mixing until just incorporated. Avoid overmixing to keep the cornbread light and fluffy.

Step 3: Assemble the Casserole

1. Lightly grease a 9×13-inch baking dish or casserole dish.
2. Spread the beef and rice mixture evenly into the bottom of the dish, pressing it down to form an even layer.
3. Pour the cornbread batter over the top of the beef mixture, spreading it out carefully to cover the entire surface.

Step 4: Bake the Casserole

1. Place the casserole in the preheated oven and bake for 20-25 minutes or until the cornbread topping is golden brown and a toothpick inserted in the center comes out clean.

Step 5: Serve

1. Remove the casserole from the oven and let it rest for 5-10 minutes before serving.
2. Cut into squares and serve warm with a side of fresh salsa, a dollop of sour cream, and a sprinkle of chopped cilantro if desired.