Preheat oven to 375 degrees.
Place spaghetti squash on a baking sheet, cut sides up. Bake for 30 minutes or until tender. Remove from oven and set aside to cool slightly.
Meanwhile, prepare sauce: Melt the ghee (or coconut oil) in a large skillet over medium-high heat. Add onion, garlic and prosciutto and cook and stir for 3 minutes. Add remaining ingredients (tomatoes through oregano).
Bring mixture to a boil then reduce heat and simmer for 10 minutes. Using a fork, scrape the squash into long, thin (spaghetti-like) strands.
Serve sauce over squash. Enjoy!