Heat a large skillet over medium high heat, add the ground meat and olive oil.
Cook - breaking up the meat as it cooks - just until it’s about halfway cooked. Add the pepperoni pieces, stir well to combine and cook for another minute or so.
Add the chopped bell pepper and onion, continue cooking until the vegetables are tender, another 2-3 minutes.
Add the remaining ingredients to the pan, stir well to combine.
Turn the heat down to medium low heat, allow to simmer for a few minutes, or until thickened to the texture you like.
Season with salt and pepper, to taste.
Split your hamburger buns, spread both sides with garlic butter. Broil for a couple of minutes, until the reach desired level of toastiness.
Divide sloppy Giuseppe mixture between your buns, top with mozzarella cheese, and serve hot!