Preheat your oven to 350 degrees F or 180 degrees C.
Cut the top off of each bell pepper and scoop out the seeds and membranes and discard them. Brush the hollowed peppers on the inside and outside with 2 tablespoons of olive oil and place them in a baking dish. Roast the peppers in the oven for about 10 minutes to make them soft. Remove the tray from the oven and set the peppers aside to cool.
In a large skillet, add the remaining tablespoon of olive oil and diced onions. Cook for about 5 minutes until the onions are soft. Add the garlic and cook for another minute.
Add the ground beef to the skillet and cook, chopping the meat as you cook into small pieces. The beef will no longer be pink once it is fully cooked, about 8 minutes.
Add the Italian seasoning, salt, and pepper to the skillet and stir the seasonings into the ground beef.
Add the diced tomatoes, cooked rice, half the mozzarella, and parmesan to the skillet and stir everything together.
Scoop the cooked beef mixture into each stuffed pepper, filling them to the top. Place the stuffed peppers back into the baking dish and sprinkle the top of each one with the shredded mozzarella cheese.
Bake the stuffed peppers for another 10 minutes to melt the cheese. Sprinkle with some fresh parsley or fresh basil. Enjoy while hot!