# Steps to Follow:
01 - In a large bowl, combine ground beef, breadcrumbs, and egg until homogenous. Shape mixture into uniform balls, approximately 1¼ inches in diameter.
02 - Arrange meatballs on a baking sheet lined with parchment paper. Bake at 400°F for 18–20 minutes until browned and cooked through, or fry in a skillet over medium heat until golden.
03 - Transfer meatballs to a saucepan with marinara sauce and simmer over low heat for 15 minutes, allowing flavors to meld.
04 - Slice sub rolls lengthwise without cutting all the way through. Toast rolls under a broiler or in the oven until lightly crisp.
05 - Layer meatballs and sauce into toasted rolls. Top generously with shredded mozzarella. Broil briefly until cheese melts and bubbles.