Preheat oven to 400°.
Combine first 7 ingredients in a large bowl. Roll into 18 (1 1/2-inch) meatballs. Dredge meatballs in breadcrumbs. Arrange meatballs on a jelly roll pan coated with cooking spray. Coat meatballs with cooking spray. Bake at 400° for 15 minutes or until done.
Pour marinara sauce into a 2-cup glass measure. Cover and microwave at HIGH 1 minute or until thoroughly heated.
Place 3 meatballs on each bun. Spoon 1/4 cup marinara sauce over each sandwich; sprinkle each with 2 tablespoons cheese. Place sandwiches on same jelly roll pan. Bake at 400° for 5 minutes or until cheese melts. Serve immediately.