Preheat broiler to high.
Gently combine first 6 ingredients in a large bowl, being careful not to overmix. Divide beef mixture into 24 equal portions; gently shape each portion into a meatball (do not pack).
Cut the mozarella crosswise into 12 thin slices.
Arrange meatballs on a broiler pan coated with cooking spray; broil 3 minutes or until browned. Turn meatballs over; broil 2 minutes or until desired degree of doneness. Arrange 2 meatballs on bottom half of each roll; top each slider with 1 cheese slice. Broil 1 minute or until cheese melts.
Heat marinara sauce until thoroughly heated, stirring once. Place two sliders on each of 6 plates; spoon about 1 1/2 tablespoons sauce over each sandwich. Top each slider with 1 basil leaf, if desired, and 1 bun top.