Preheat your oven to 375°F (190°C).
Cut the tops off the bell peppers and remove the seeds and membranes. Arrange the peppers upright in a baking dish.
In a skillet over medium heat, add the olive oil. Once hot, add the chopped onion and minced garlic. Sauté until the onion is translucent (about 3-4 minutes).
Add the ground beef to the skillet. Cook until browned, breaking it apart with a spoon as it cooks (about 5-7 minutes).
Stir in the uncooked rice, diced tomatoes (with their juice), oregano, paprika, salt, and pepper. Mix well and let it simmer for about 5 minutes until the mixture is heated through.
Remove the skillet from the heat and stir in half of the shredded cheese.
Stuff each bell pepper with the beef and rice mixture, pressing down lightly to pack it in.
If desired, top the stuffed peppers with the remaining shredded cheese.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 5 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let them cool slightly. Garnish with fresh parsley if using, and serve warm.