Preheat oven to 375 degrees. With a small sharp knife, prick squash all over. Place on a rimmed baking sheet and roast until tender when pierced with knife, about 1 hour 20 minutes, flipping halfway through. When cool enough to handle, halve lengthwise and scoop out seeds. Scrape squash with a fork to remove flesh in long strands.
Refrigerate squash in an airtight container, up to 3 days.