Preheat the oven to 375°F (190°C).
Bring a large pot of water to a boil. Add the bell peppers and boil 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 for 3 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet. Cook, breaking it up with a spoon, until browned and cooked through, about 6-8 minutes. Drain excess fat if necessary.
Stir in the cooked rice, black beans, diced tomatoes, ground cumin, chili powder, smoked paprika, salt, and black pepper. Cook for 3-4 minutes until heated through and well combined.
Remove the skillet from heat and stir in half of the shredded cheddar cheese.
Place the bell peppers upright in a baking dish. Spoon the beef and rice mixture evenly into each pepper, pressing down gently to fill completely.
Sprinkle the remaining shredded cheddar cheese evenly over the tops of the stuffed peppers.
Cover the baking dish with aluminum 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.
Garnish with chopped fresh cilantro and serve with salsa on the side.