Heat oven to 475°F. Lightly grease baking sheets.
In medium bowl, stir together Krusteaz Italian Herb Flatbread Mix and yeast (enclosed). Add warm water and oil, stirring until dough forms a ball. To activate yeast, cover dough and let rest 10-20 minutes, or until oven is hot. Shape dough by dividing into 8 portions. With floured hands, pat out dough 1/8 -1/4-inch thick, forming circle on prepared pan(s).
On one half of dough, place sliced meatballs and 1/4 cup cheese. Fold dough over to create calzone. Press edges to seal.
Bake 8-10 minutes or until edges are golden brown. Brush lightly with olive oil, if desired. Serve with heated marinara sauce.