Preheat oven to 400°F (200°C)
Line a baking sheet with parchment paper
Cut spaghetti squash in half lengthwise
Scoop out seeds and stringy pulp
Brush cut sides with olive oil
Sprinkle with salt and pepper
Place squash cut-side down on the baking sheet
Roast for 35–50 minutes, until tender and easily pierced with a fork
Remove from oven and let cool 5–10 minutes
Use a fork to scrape the flesh into spaghetti-like strands
Toss strands with butter or olive oil, plus garlic, herbs, or Parmesan if desired
Serve immediately