In large bowl, mix beef, bread crumbs, milk egg, salt and pepper with hands until well combined. Shape mixture into small balls about the size of a Ping-Pong ball.
With finger, make hole in 1 ball but do not go all the way through. Place 1 piece of cheese in hole; enclose cheese by pinching hole back together. Repeat with remaining beef mixture and cheese pieces.
Spray 3 1/2- to 4-quart slow cooker with cooking spray. Pour pasta sauce into cooker. Place meatballs in sauce.
Cover; cook on Low heat setting 4 hours.
About 25 to 30 minutes before meatballs are done, cook pasta as directed on package; drain.
Try switching out the mozzarella cheese sticks with ones of sharp Cheddar cheese or Colby-Monterey Jack cheese blend.
Add a teaspoon each of garlic powder, onion powder and parsley flakes to the beef mixture for an even bigger boost of flavor!