Preheat the oven to 375°F (190°C).
Prepare the peppers: Cut the bell peppers in half and remove the seeds and membranes. Rinse under cold water and set aside.
Cook the rice: In a medium saucepan, bring the broth to a boil. Add the rice, reduce the heat to low, cover, and simmer for about 15 minutes, or until the rice is tender and the liquid is absorbed. Remove from heat and fluff with a fork.
Prepare the filling: Heat the olive oil in a large skillet over medium heat. Add the chopped onion and cook until softened about 5 minutes. Add the garlic and cook for another 1-2 minutes until fragrant.
Cook the meat: Add the ground beef (or Italian sausage) to the skillet. Cook until browned and fully cooked, breaking it up with a spoon as it cooks. Drain any excess fat.
Combine ingredients: Add the diced tomatoes, cooked rice, and Italian seasoning to the skillet. Season with salt and pepper to taste. Stir to combine and heat through for about 2-3 minutes.
Stuff the peppers: Spoon the filling into the prepared bell peppers, packing it down gently.
Bake: Place the stuffed peppers in a baking dish and cover with foil. Bake in the preheated oven for 30 minutes.
Add cheese: Remove the foil and sprinkle the tops of the peppers with mozzarella and Parmesan cheese. Return to the oven and bake for an additional 15 minutes, or until the cheese is melted and bubbly.
Serve: Garnish with fresh basil or parsley if desired. Serve hot.