Line a small baking sheet with foil and mist lightly with cooking spray.
Place milk and bread crumbs in separate shallow bowls.
Dip cheese pieces in milk, rolling to moisten completely. Dredge in bread crumbs to cover entire surface and place on baking sheet. Mist with cooking spray. Freeze for 1 hour.
Preheat oven to 400F.
Bake mozzarella sticks until bread crumbs are browned and cheese begins to ooze, 6 to 7 minutes.
Let stand 3 minutes.
Microwave marinara sauce in a small bowl until warm, 20 to 30 seconds.
