How to Roast Spaghetti Squash Trim both ends with a chef's knife, then position the squash upright and halve lengthwise. Scoop out the seeds with a spoon and discard. Place the squash halves cut-side down on a baking sheet. Roast at 400 degrees F until tender, 25 minutes; let cool slightly, Scrape the squash into strands with a fork. Discard the skin. Cook's Note: Refrigerate the extra pesto up to 1 week or freeze up to 1 month.