Heat the oven to 400°F. Wash and dry the spaghetti squash, then place it on a stable cutting board.

Carefully cut the squash in half lengthwise and scoop out the seeds and stringy pulp. If the squash is unusually difficult to cut, pierce it several times and microwave it for 3 to 5 minutes, then let it cool briefly before cutting; never microwave it unpierced.

Brush the cut surfaces with olive oil and sprinkle evenly with kosher salt and black pepper. Add the optional garlic powder or minced garlic if desired.

Place the squash halves cut-side down on a rimmed baking sheet. Roast for 40 to 50 minutes, depending on the size of the squash.

Check for doneness when a fork easily pierces the skin and the flesh separates into strands. Remove the squash before it becomes mushy, since overbaking can create watery strands.

Let the baked squash rest for 5 to 10 minutes so it is easier to handle and the steam can settle. Use a fork to gently scrape from the outside toward the center, separating the flesh into spaghetti-like strands.

Taste the strands and adjust the seasoning with more salt, pepper, olive oil, butter, Parmesan, or herbs. Toss with marinara, pesto, or another sauce and serve warm.