Carefully cut the spaghetti squash in half lengthwise and scoop out the seeds using a spoon.
Drizzle the inside of each half with half of the olive oil and sprinkle with salt and black pepper.
Place the squash, cut side up, on a baking sheet lined with parchment paper.
Roast in the preheated oven for about 40-45 minutes, or until the flesh is tender and easily pierced with a fork.
While the squash is baking, in a small saucepan, heat the remaining olive oil over medium heat. Add the minced garlic and red pepper flakes (if using) and cook for 1-2 minutes until fragrant but not browned. Remove from heat.
Once the squash is done, use a fork to scrape the flesh into strands. Combine the spaghetti squash strands in a large bowl.
Pour the garlic oil mixture over the squash and toss to coat. Add the grated Parmesan cheese and mix until well combined.
Transfer the mixture back into the squash halves and sprinkle additional Parmesan cheese on top.
Return to the oven and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly.
Remove from the oven and garnish with fresh parsley before serving.
Notes
Feel free to adjust the amount of red pepper flakes based on your spice preference.