Preheat your oven to 350 degrees Fahrenheit. This ensures that your peppers will cook evenly and thoroughly.
In a large pot over medium heat, pour in the olive oil. Once it’s hot, add the onion and garlic. Sauté them until the onion becomes translucent and the garlic turns golden, then remove the garlic and discard it; it’s done its job of flavoring the oil.
Now, add the ground beef to the pot. Using the back of a spoon, break it down into smaller pieces. Cook it until there are no juices left, and the beef is browned completely.
Stir in the tomato sauce, adding a sprinkle of salt and pepper to taste. Lower the heat, cover, and let it simmer for about 20 minutes. This allows the flavors to meld beautifully.
While the sauce is cooking, slice the bell peppers in half lengthwise. Carefully remove all the seeds and membranes. Rinse them under cold water, then dry them with a paper towel. Sprinkle the insides with a little salt and pepper.
Butter an ovenproof pan to prevent sticking. Arrange the bell pepper halves in the pan, cut side up.
Once the tomato mixture is ready, mix in the cooked white rice, parmesan cheese, and mozzarella. Stir until everything is well combined, creating a filling that’s bursting with flavor.
Now, it’s time to fill each bell pepper half with the mixture. Pack it in but don’t overfill them, as the cheese needs space to melt.
Sprinkle the remaining parmesan cheese over the tops of the stuffed peppers. This will create a lovely cheesy crust while baking.
Carefully place the pan in your preheated oven and bake for 20 to 25 minutes. You’ll know they are done when the cheese is melted and bubbly, and the peppers are slightly soft.