Mix the beef, crackers, onion, garlic, and flaxseed or whey powder into golf ball-size meatballs.
In a nonstick skillet over medium heat, cook the meatballs until browned all the way around. Drain the fat from the skillet, and add the tomato sauce.
While the mixture is warming, use a fork to scoop out some of the bread in the rolls to form shallow trenches. Spoon the meatballs and sauce into each trench, and sprinkle with shredded mozzarella, and top with the top half of the roll.