1.Cut mozzarella into 3/4 inch cubes and place back into the refrigerator.
2.In a large bowl add beef, sausage, garlic powder, salt, pepper, bread crumbs, Parmesan, eggs, milk, and parsley. Using hands, gently mix together until just incorporated, make sure not to overmix.
3.Take mozzarella out of the fridge. Start rolling golf ball sized balls with the meat mixture. Place mozzarella cube into the center and pull the edges of the meat around the cheese, until it is completely covered with meat. Roll back into a ball and place into a slow cooker. Repeat until meat mixture is gone.
4.Empty the jar of spaghetti sauce on top of the meatballs. Cook on high in slow cooker for 2 hours. Serve immediately.