In a large stock pot, cook onion and garlic in olive oil over medium high heat until translucent. Stir in tomato sauce, water, rice, mint, and salt, and bring to a low boil.
Meanwhile, combine ground sirloin with tomatoes, 2 tablespoons diced onion, egg white, mint, and salt and pepper. Form into small balls, and place in boiling liquid. Reduce to a simmer, cover, and cook for 30 minutes, or until meat is cooked and rice is tender.