01 - Set the oven temperature to 375°F.
02 - Bring a large pot of salted water to a boil. Immerse the bell peppers for 3 minutes. Drain and invert to dry.
03 - Heat olive oil in a skillet over medium heat. Cook chopped onion for 3 to 4 minutes until softened, then add minced garlic and cook for 1 more minute.
04 - Add ground beef to the skillet, breaking it apart. Cook until fully browned. Drain excess fat if necessary.
05 - Incorporate diced tomatoes, cooked rice, half of the cheese, parsley, oregano, salt, pepper, paprika, and optional red pepper flakes into the beef mixture. Cook for 2 to 3 minutes until heated through and well combined.
06 - Place blanched peppers upright in a baking dish. Fill each pepper evenly with the beef and rice mixture.
07 - Sprinkle the remaining shredded cheese on top of each filled pepper.
08 - Pour ¼ cup water into the bottom of the baking dish. Cover loosely with aluminum foil.
09 - Bake the peppers for 30 minutes in the preheated oven.
10 - Remove the foil and bake for another 10 to 15 minutes until the cheese is golden and peppers are tender.
11 - Allow the peppers to cool slightly for a few minutes before serving.