Preheat your oven to 425 degrees.
Spray a cookie sheet with non-stick cooking spray.
Rinse the exterior of the squash, since you'll be roasting it in the skin.
Slice the stem-end off, and then cut it lengthwise down the center. Scoop out the seeds and stringy matter.
Place the squash face-up on a cookie sheet, drizzle with olive oil, and sprinkle with salt and pepper (you can omit the pepper if preparing the squash for a sweet recipe). Then turn the squash face-down, directly onto the cookie sheet.
Roast for 45-60 minutes, or until it is soft throughout the body of the squash. (The roasting time can vary, depending on the size of the squash.)
Remove and allow to cool for a few minutes.
Scrape out the flesh onto a plate and mash it. (You can also puree it in a blender, if you prefer a super creamy texture.) It is now ready to be used in a recipe, or stored in the refrigerator or freezer!