Preheat the Oven: Start by preheating your oven to 375°F (190°C).
Prepare the Chiles: Roast the chiles on an open flame or under the broiler until they’re charred. Place them in a sealed bag for about 10 minutes to steam, then peel off the skins. Cut a slit in each one to remove the seeds and membranes.
Make the Filling: In a large bowl, combine cooked rice, black beans, corn, half of the shredded cheese, salsa, cumin, garlic powder, salt, and pepper. Mix until well combined.
Stuff the Chiles: Carefully fill each roasted chile with the prepared mixture.
Assemble the Casserole: In a greased baking dish, spread a layer of salsa on the bottom. Place the stuffed chiles on top and pour remaining salsa over the top. Sprinkle with the remaining cheese.
Bake: Cover the dish with foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes until cheese is melted and bubbly.
Garnish and Serve: Allow to cool slightly, then top with sour cream and fresh cilantro, if desired. Enjoy!