Preheat the oven to 375°F (190°C).
Bring a large pot of water to a boil. Add the bell peppers and cook for 3 minutes to soften slightly. Remove and drain upside down on paper towels.
Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook until softened, about 3 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet and cook until browned, breaking it apart with a spoon, about 6-8 minutes.
Stir in ground cumin, chili powder, smoked paprika, salt, and black pepper. Cook for 1 minute to toast the spices.
Add the cooked rice, black beans, corn, and diced tomatoes to the beef mixture. Stir well and cook for 2-3 minutes until heated through.
Remove the skillet from heat and stir in half of the shredded cheddar cheese and chopped cilantro.
Place the bell peppers upright in a baking dish. Spoon the beef and rice mixture evenly into each pepper, packing gently.
Sprinkle the remaining shredded cheddar cheese on top of each stuffed pepper.
Cover the baking dish with foil and bake for 25 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let cool for 5 minutes before serving.