Preheat oven to 400°F and line a baking sheet with parchment paper.
Cut the spaghetti squash in half lengthwise, scoop out the seeds, and brush the cut sides with 2 tablespoons of olive oil, then season with salt and pepper.
Place the squash cut-side down on the baking sheet and roast for 35-40 minutes until tender and easily pierced with a fork.
Let the squash cool for 5 minutes, then use a fork to scrape out the spaghetti-like strands into a large bowl.
In a large skillet, heat the remaining olive oil and butter over medium heat, add the garlic and cook for 1 minute until fragrant.
Add the spaghetti squash strands to the skillet and toss to coat with the garlic butter, cooking for 2-3 minutes.
Remove from heat, stir in the Parmesan cheese and fresh parsley, season with additional salt and pepper if needed, and serve immediately.