Preheat your oven to 425 degrees F. Line a rimmed baking dish with high-heat-resistant parchment paper.
Pierce the squash in a few places with a fork and microwave it for 1 minute, to slightly soften.
Using a large, sharp knife, cut the squash in half lengthwise. Place it on a sturdy cutting board, and work very carefully. First slice off the stem end of the squash, then stand the squash upright on this flat end and carefully use your knife to slice it in half.
Using a large metal spoon, remove the seeds and pulp.
Lightly spray the cut side with olive oil and, if you wish, sprinkle it with salt and pepper.
Place the squash halves, cut side down, in the prepared baking dish. Bake until fork-tender, about 40 minutes.
Transfer the cooked squash to a cutting board and allow it to cool until easier to handle, for about 10 minutes.
Rake a fork back and forth across the squash to remove its flesh in strands, transferring the strands to a bowl. Use as a side dish (try mixing melted butter, garlic granules and grated parmesan into the hot strands) or as the basis for other recipes.
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Notes
Overcooked spaghetti squash can become mushy. You can start checking on it after about 30 minutes in the oven. As soon as it can be easily pierced with a fork, pull it out of the oven. Although the strands won't be as perfect as when they first emerge out of the oven, you can reheat cooked spaghetti squash, either in the microwave or in a low oven. In fact, if your squash ended up mushy, spreading the strands evenly on a baking sheet and reheating them in a 300F oven is a good way to improve their texture.