Preheat oven to 375°F (190°C). Rinse peppers, pat dry, and slice off the tops. Remove seeds and white membrane. Lightly brush the outside with olive oil, season the insides with salt and pepper, and stand upright in a 9x13-inch baking dish.
In a medium saucepan, combine the rice and beef broth. Bring to a boil, then reduce to a simmer. Cover and cook for 15-18 minutes until liquid is absorbed. Remove from heat and let sit for 5 minutes before fluffing.
Heat olive oil in a large skillet over medium-high heat. Add the onion and cook for 3-4 minutes until softened. Add garlic and cook for 30 seconds. Add ground beef and cook for 6-8 minutes until browned, breaking it up as it cooks. Drain excess fat.
Season the meat with Italian seasoning, garlic powder, onion powder, smoked paprika, salt, and pepper. Stir in the diced tomatoes, tomato sauce, and Worcestershire sauce. Let simmer for 3-4 minutes. Stir in the cooked rice and remove from heat. Mix in 1 cup of the mozzarella cheese.
Spoon the filling into each prepared pepper, packing it firmly and mounding it slightly. Drizzle extra tomato sauce over the top of each pepper.
Pour 1/2 cup of water into the bottom of the baking dish around the peppers. Cover tightly with aluminum foil and bake for 35 minutes.
Carefully remove the foil. Sprinkle the remaining mozzarella and the cheddar cheese evenly over the tops of the peppers. Return to the oven, uncovered, and bake for 10-15 minutes until the cheese is melted and bubbly.
Remove from oven and let rest for 5 minutes before serving. Garnish with fresh chopped parsley if desired.