1. Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper. Slice the spaghetti squash in half lengthwise and scoop out the seeds. Drizzle each half with 1 tablespoon olive oil. Sprinkle with salt, pepper, and 1/2 teaspoon Italian seasoning. Place squash halves cut side down on the baking sheet. Roast for 35-40 minutes, or until fork-tender. While the squash is roasting, heat a large skillet over medium heat. Add remaining olive oil, onion, and garlic. Sauté for 2-3 minutes until fragrant. Add ground beef and cook until browned, breaking it up with a spoon. Stir in crushed tomatoes, remaining Italian seasoning, salt, pepper, and red pepper flakes if using. Simmer for 10 minutes, stirring occasionally. Remove squash from oven and let cool slightly. Turn squash halves cut side up and use a fork to gently scrape the flesh into spaghetti-like strands, keeping them inside the shell. Spoon meat sauce evenly into each squash half and mix lightly. Sprinkle with mozzarella and Parmesan cheese. Return squash halves to oven and bake for 10-12 minutes, until cheese is melted and bubbly. Garnish with chopped fresh parsley and serve hot.