Heat 2 tbsp olive oil in a large skillet over medium-high heat. Cook the diced onion for 3 minutes, then add 1 lb ground beef and cook 5 to 6 minutes until no pink remains. Add 3 cloves minced garlic, 1 tsp oregano, 1 tsp smoked paprika, ½ tsp salt, and ½ tsp black pepper; cook 1 more minute, then drain excess fat.

Stir 1 can drained diced tomatoes and 1 cup uncooked white rice into the beef mixture off the heat until evenly combined.

Preheat oven to 375°F (190°C). Slice the tops off 6 bell peppers, remove seeds and membranes, and stand them in a snug baking dish. Divide the filling evenly among the peppers, pressing it down gently.

Mix 1 can crushed tomatoes, 1 cup beef broth, and remaining ½ tsp salt; pour around and over the peppers. Cover the dish tightly with foil and bake at 375°F (190°C) for 45 minutes.

Remove the foil, spoon sauce over the pepper tops, scatter 1 cup shredded mozzarella over the peppers, and bake uncovered for 10 to 12 minutes until the cheese is melted and browned. Garnish with fresh chopped parsley and serve straight from the dish.