Preheat oven to 375 degrees F.
Cut the tops off the tomatoes and, using a spoon, hollow out the middle. In a medium bowl, combine the mozzarella, bread crumbs, parsley, garlic, oregano, and olive oil. Season to taste with salt and pepper. Place the stuffing in the tomatoes, taking care not to pack them too tight. Place on a baking sheet and transfer to the oven. Roast for 30 minutes.