Wash your hands. Scrub the whole spaghetti squash under running water with a clean produce brush, then pat it dry with a clean towel. Do not use soap or detergent on the squash.

Heat the oven to 400°F (200°C) with a rack in the middle. Line the rimmed 13 × 18-inch half-sheet pan with parchment rated for that temperature.

Set the squash securely on a steady cutting board. Carefully cut it lengthwise into two halves with a sharp chef's knife, keeping fingers clear and using controlled cuts beside the hard stem rather than forcing through it. If you cannot cut it steadily, stop and use fresh precut halves. Scoop out the seeds and loose stringy center with the large spoon.

Rub the cut flesh of both halves with the measured olive oil. Sprinkle with the salt and black pepper. Place cut-side down on the prepared pan; do not add water.

Roast for 40–50 minutes, checking at 35 minutes if the squash is small. Wearing oven mitts and using a spatula or tongs, carefully turn a half cut-side up, keeping your face away from escaping steam. Test the flesh with a fork: it should release into strands that are tender but retain a little bite. If still firm, return cut-side down and check again after 5 minutes. Larger squash may need longer.

Let the halves cool for about 10 minutes, or until safe to handle. Use a fork to gently loosen the flesh into strands. Transfer to a serving bowl, taste the seasoning and serve plain or add a sauce gradually. Do not eat the hard rind.