Heat a large oven proof skillet and add your ground beef to it.
Season with salt and pepper and cook 5 minutes, stirring so the beef is in fine pieces rather than large chunks.
Add the marinara sauce and cook for 3 minutes.
Add the spaghetti squash and parmesan cheese and stir well to combine.
Top with the shredded mozzarella.
Bake at 375 degrees for 20 minutes or until the cheese is melted and turning golden brown.
Serve garnished with chopped fresh basil or parsley if desired.