Line a baking sheet with parchment paper or aluminum foil.
Place the spaghetti squash on baking sheet and bake for 15 minutes, or soft enough to cut. Puncture the squash several times with a sharp knife if you're worried about it exploding in the oven. This has never happened to me and I don't *think* it's in the oven long enough to explode before cutting, but feel free to puncture it if you're worried about it.
Carefully slice the squash in half lengthwise (or width-wise, either will work) with a sharp knife.
Drizzle the squash with olive oil and lightly season with salt and pepper if desired.
Place flesh side down and continue roasting for 15 - 25 minutes, depending on size of squash. If your squash is particularly small, check after 10 minutes just to ensure you don't overcook it. To check for doneness, flip one half of the spaghetti squash over and run a fork down the top edge of the squash. The squash is done cooking when the fork easily forms spaghetti-like strands with an al-dente (slightly firm) texture. Do not over cook or it will be mushy and ruin the dish!
Once done, allow to cool enough to handle. Scoop out the seeds and discard them. Then use a fork to gently scrape out the flesh, the squash will come out in noodle-like strands.