Preheat oven to 375 degrees F and get large baking sheet.
Using a paring knife, pierce spaghetti squash about 15 times. Place on a baking sheet and cook for 45 minutes, turning once. The actual cook time will depend on the size of squash, from squash to squash and your oven.
Remove from the oven, place on a cutting board and let cool for 20 minutes.
Wearing an oven mitt, hold the squash and cut lengthwise. Scoop out the seeds and flesh, discard. Now let squash cool down for 10 more minutes.
Using a fork, separate squash into "noodles" and place in a bowl. Use a fork or spoon to run it inside the squash to get all the flesh out.
Notes
Store: Refrigerate in an airtight container for up to 5 days. If you find water has pooled at the bottom, just drain it.
Microwave: Pierce outer skin multiple times to let steam escape, place in square baking dish and cook 10-12 minutes. Check for doneness, then remove to cool.
Slow cooker: Pierce outer skin multiple times to let steam escape. Place in slow cooker with 1/4 cup of water and cook on high 3-4 hours or low 5-6 hours. Test for doneness, then remove to cool.