Cut each string cheese into 8 equal pieces - freeze until time to form meatballs.
Preheat oven to 500°F.
Combine beef, breadcrumbs, milk, eggs, onion, garlic, salt and pepper in large bowl.
Shape into 1 to 1 1/2 inch meatballs, around each piece of frozen mozzarella. Seal meatballs well to keep cheese from oozing out.
Mix sauce ingredients together and set aside.
Place meatballs closely together on lightly greased broiler pans or rimmed baking sheets. Bake for 15 minutes and cool (if planning to freeze); around 30 minutes if planning to eat right away.
Add sauce to last 15 minutes of baking if cooking that day. If freezing meatballs, add sauce to freezer bag and add cooked, cooled meatballs to it.
If cooking after freezing - thaw completely.
Preheat oven to 350°F.
Pour meatballs and sauce into ungreased baking dish. Bake uncovered for 30 minutes or until meatballs are heated through. Serve over rice or noodles.