In a medium bowl...whisk egg, garlic, parmesan, salt, pepper, milk.
Add in ground beef and combine with your hands just until incorporated.
Shape into 1 inch size balls.
Over med/high heat, add oil to pan. In batches, brown the outside of the balls.
When all are browned, add sauce in the pan, turn to low and cover and simmer for 15-30 minutes.
Brown buns under broiler. Melt cheese on the top. Add meatballs to your sub!