Preheat the oven to 400 degrees. Place the spaghetti squash halves cut side up on a baking sheet. Brush the flesh with 1 tablespoon olive oil and season lightly with salt and pepper. Roast for 35 to 40 minutes until the strands are tender when scraped with a fork.
While the squash roasts, combine the ground turkey, grated zucchini, egg, breadcrumbs, minced garlic, oregano, salt, and black pepper in a large bowl. Mix gently until just combined, then form the mixture into 16 meatballs.
Heat the remaining tablespoon of olive oil in a large skillet over medium heat. Add the meatballs and cook for 8 to 10 minutes, turning occasionally, until browned on all sides and cooked through to 165 degrees.
Warm the marinara sauce in a small saucepan over low heat while the meatballs finish cooking.
Scrape the roasted squash into strands and divide among four plates. Top each portion with meatballs and sauce, then sprinkle with chopped parsley and Parmesan cheese before serving.