1. Preheat the oven to 400 degrees. Line a baking sheet with foil.
  2. Cut spaghetti squash in half and scoop out center of seeds. Place on baking sheet with foil.
  3. Drizzle with olive oil. Season with garlic powder, salt and pepper. Bake for 40 minutes.
  4. While squash cooks, heat a small skillet over medium heat. Chop pepperoni and place into skillet. Cook until crisp.
  5. When squash is done, remove from oven. Loosen spaghetti squash strands with a fork. Mix in half of the pizza sauce or marinara, half of the mozzarella, and half of the pepperoni. Top each squash half with remaining mozzarella. Place in oven until cheese is melted and bubbly. Top with remaining sauce, pepperoni, and parsley if desired.