Step 1: Preheat your oven to 375°F (190°C). Lightly grease a large baking dish.
Step 2: Wash the banana peppers thoroughly. Carefully slice each pepper lengthwise and scoop out the seeds and membranes. Be gentle to keep the pepper intact.
Step 3: In a large skillet, heat olive oil over medium heat. Add the chopped onion and cook until softened, about 5 minutes. Add the minced garlic and cook for another minute until fragrant.
Step 4: Add the ground meat to the skillet. Break it up with a spoon and cook until browned, about 8-10 minutes. Drain any excess fat.
Step 5: Stir in the cooked rice, diced tomatoes (undrained), tomato paste, Italian seasoning, salt, and black pepper. Mix everything until well combined. Cook for 5 minutes, allowing the flavors to meld. Remove from heat and stir in half (1/2 cup) of the shredded mozzarella and all of the Parmesan cheese.
Step 6: Carefully spoon the filling into each banana pepper half. Don't overfill, but make sure they're generously packed. Arrange the stuffed banana pepper halves in your prepared baking dish, seam-side up.
Step 7: Pour the vegetable broth or marinara sauce around the peppers in the baking dish. Cover the baking dish tightly with aluminum foil.
Step 8: Bake for 30 minutes. Remove the foil, sprinkle the remaining 1/2 cup of mozzarella cheese over the stuffed banana peppers, and bake for another 15-20 minutes, or until the peppers are tender and the cheese is melted and bubbly.
Step 9: Garnish with fresh parsley, if desired, and serve hot.