Preheat oven to 400 degrees F. Line a baking sheet with parchment paper or if you have a nonstick baking sheet, lining is not necessary.
Divide the dough in 4 equal portions. Place on a floured work surface and using a rolling pin, roll out the dough into a small round about 6 to 8 inches in diameter. Repeat with remaining pieces of dough. Set aside.
Place about a quarter of the leftover Spaghetti with Meatballs in the center of the dough round. Top with 1 tablespoon of sauce and sprinkle with a tablespoon of cheese. Brush the edges of the dough with a bit of water. Fold the dough over to make a half circle and crimp the edge with a fork. Place on prepared baking sheet. Repeat with remain filling and dough.
Place in oven and bake for 35 minutes or until golden brown. Serve hot with a side of Tomato Sauce.
Spaghetti with Meatballs:
Preheat oven to 400 degrees F.
In a large bowl combine the milk and bread. Let the bread absorb the milk. Add remaining meatball ingredients except the cheese. Using your hands, gently combine all the ingredients until they are thoroughly mixed. Take about 3 tablespoons of the meat mixture and roll into a ball and press into a patty. Place a mozzarella cube or 1 tablespoon shredded cheese onto the patty and bring up the sides around the cheese and roll between hands to form a ball. Place onto a nonstick baking sheet or a baking sheet sprayed with nonstick cooking spray. Repeat process with remaining meat and cheese. Place the meatballs into the oven and cook for 12 minutes. Remove baking sheet from the oven and set aside.
Cook the spaghetti in a large pot of boiling salted water until al dente, about 8 minutes. Drain and place the pasta on a large serving platter.
In a medium pot heat olive oil over medium heat. Add onion, garlic and saute for 3 minutes. Add remaining ingredients and simmer for 10 minutes. Gently stir in the meatballs and any pan drippings from baking sheet and simmer for another 5 minutes.
Place the meatballs over the spaghetti, pour the sauce on top and serve immediately.