Heat the oven to 400 degrees F. Unfold the pastry sheets on a lightly floured surface. Cut each pastry sheet into 16 (2 1/2-inch) squares. Place the pastry squares onto 2 baking sheets.
Bake for 15 minutes or until the pastries are golden brown. Let cool on the baking sheets for 5 minutes. Split each pastry into 2 layers, making 64 layers in all.
Heat the meatballs according to the package directions. Spread about 1 teaspoon pasta sauce on each bottom pastry layer. Top each with 1 tablespoon arugula and 1 meatball. Top with the cheese, if desired, and the top pastry layers.