In a large bowl combine ground beef, rice, onion, garlic, Pecorino Romano, basil, egg, 3 tablespoons crushed tomato and 1¼ teaspoons kosher salt and mix well with a fork.
Combine remaining crushed tomato, water and remaining salt in the base of a large saucepan large enough to fit the peppers standing up.
Fill each bell pepper with 1 cup of mixture and nestle the stuffed peppers into the sauce. Ladle a little sauce over each.
Cover and cook the peppers on medium-low heat for 35-45 minutes, until the peppers are tender and the meat is cooked through in the center.
Ladle more sauce over each and add 2 tablespoons of mozzarella cheese to the top of each pepper, cover and cook until melted, about 5 minutes.
