First, cut the ends off the spaghetti squash using a heavy knife, rocking it back and forth with control. Cutting off the ends helps stabilize the squash so you have more leverage and stability, which makes it safer to cut the squash in half lengthwise.
Turn the squash onto one of its flat sides, then cut a notch midway into the top. Stabilize the squash with your non-knife hand, like below, and guide the knife through the rest of the gourd length-wise.
Scrape out the seeds and any pulpy strings with a spoon. Just like most winter squashes, the inside is hollow, filled with seeds and some stringy fibers; you can roast the seeds like pumpkin seeds if you wish.
Place the halves cut side down in a 9x13-inch baking pan, add ¾ cup of water, and roast for 45 to 55 minutes until the halves look somewhat wrinkly and slightly collapsed, and the squash itself is tender. Check as the cooking time gets towards the end to make sure there is still a bit of water in the pan, adding more if necessary.
Remove the squash from the oven and allow to cool about 15 minutes.
Using a fork, scrape, scrape, scrape the inside of the squash to release the insides from the skin (you may want to hold the squash with a dishtowel as it will still be quite hot. You’ll see the squash form spaghetti-like strands as you do this; it’s pretty cool. Transfer all of the squash to a serving bowl (or individual bowls), then use it or top it as you wish. Toss the outside shells.
Notes
Look for spaghetti squash that has an even color all over the gourd, with no dings, cuts, or dark spots. And pick it up — you’re looking for a squash that feels heavy for its size, meaning there is a lot of firm flesh inside.