Preheat the oven to 400 degrees F. Fill a baking dish with 1/2-inch of water and place the spaghetti squash flesh side down. Bake until tender, about 20 - 30 minutes.
While the squash is baking, prepare the meatballs by adding all the remaining ingrediens (aside from the sauce) into a mixing bowl. Form the meat into meatballs (about 1-inch wide), and place them on a parchment paper lined baking sheet about 1 inch apart. Place on the lower shelf of the oven and bake for 15 - 20 minutes, rotating the meatballs halfway through.
Remove the meatballs and squash from the oven and let cool for a few minutes. Scrape the squash out of the skin with two forks and serve into bowls. Top with tomato sauce and meatballs, sprinkled with fresh grated cheese.