Preheat the oven to 375°F (190°C).
Bring a large pot of water to a boil. Add the bell peppers and blanch for 3 minutes to soften slightly. Remove and drain on paper towels.
Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook for 3-4 minutes until softened.
Add the minced garlic and cook for 1 minute until fragrant.
Add the ground beef to the skillet. Cook, breaking it apart with a spoon, until browned and cooked through, about 6-8 minutes. Drain excess fat if necessary.
Stir in the cooked rice, diced tomatoes, dried oregano, ground cumin, smoked paprika, salt, and black pepper. Cook for 2-3 minutes until heated through and well combined.
Remove the skillet from heat and stir in the chopped fresh parsley.
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 shredded cheddar cheese evenly over the stuffed peppers.
Cover the baking dish with aluminum foil and bake for 30 minutes.
Remove the foil and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly and the peppers are tender.
Remove from oven and let cool for 5 minutes before serving.