All you need is the squash, olive oil, and salt and pepper. Slicing crosswise into rings keeps the squash strands long and spaghetti-like.
Preheat oven to 400 degrees with racks in upper and lower thirds. Arrange squash slices on 2 wire racks set over rimmed baking sheets. Generously season each side with salt; let stand 20 minutes.
Pat each slice dry with a paper towel. Clean sheets and wipe dry; rearrange slices on them. Brush both sides with oil, season with pepper, and roast until caramelized and tender, about 40 minutes.
Peel skin away; separate strands into long "noodles." Cooked squash can be refrigerated in an airtight container up to 2 days.