Preheat the oven to 350°F. Grease a 9×13 baking dish.

Dice the onion and chop the cilantro.

In a large skillet, cook the ground beef with the onion over medium heat, breaking it apart as it cooks. Drain any grease.

Add the corn, black beans, diced tomatoes, green chiles, rice, water, and taco seasoning. Stir to combine, then fold in half of the cheese.

Pour the mixture into the prepared casserole dish and spread evenly. Top with the remaining cheese.

Bake for 25 minutes, or until the rice is tender. Let it set for 5 minutes before serving.

Sprinkle with cilantro and serve with sour cream, if desired.