Preheat oven to 400 degrees F. Line a rimmed baking sheet with parchment paper.
Prepare the spaghetti squash: Pierce the spaghetti squash in a few spots with a sharp knife. Microwave 5 minutes; turn to the other side and microwave 5 more minutes, until soft to the touch. Let stand for 5 minutes to finish cooking. Using a sharp knife, cut the spaghetti squash in half lengthwise. Allow to cool 5 minutes, until easier to handle. Scoop out the pulp and seeds from the center, then rake a fork back and forth to remove strands of the flesh onto a serving bowl. Set aside.
Prepare the meatballs: In a medium bowl, mix together the beef with the salt, pepper, garlic powder, onion powder, smoked paprika and oregano. Form into 24 small meatballs. Place the meatballs on the prepared baking sheet. Bake 10 minutes, until juices run clear and an instant-read thermometer inserted in a meatball reads 160 degrees F.
Heat the marinara sauce in a large saucepan over medium-low heat. When meatballs are ready, transfer them to the warm sauce and continue to simmer for 5 more minutes.
Pour the meatballs and sauce on top of the spaghetti squash strands, garnish with parsley and (if using) parmesan, and serve.