Preheat the oven to 375°F (190°C).
Slice the tops off the poblano peppers and remove the seeds.
In a large bowl, mix cooked rice, black beans, corn, diced tomatoes, cumin, chili powder, salt, and pepper.
Stuff each poblano pepper generously with the rice mixture.
Place the stuffed peppers in a baking dish.
Sprinkle shredded cheese on top of each pepper.
Cover the dish with foil and bake for 20 minutes.
Remove the foil and bake for an additional 10 minutes until cheese is bubbly and golden.
Let cool for a few minutes before serving.
Garnish with fresh cilantro.