Use a paring knife to make several slits in the skin of the spaghetti squash, along the line where you will cut it in half lengthwise. Cook in the microwave for 4 to 5 minutes on high to soften (you MUST make slits before putting it in the microwave to let steam escape).
Remove the squash from the microwave, using a dish towel or oven mitt. Cut the squash in half lengthwise along the slits you made, and slice off the stem. Remove and discard the seeds.
Preheat the oven to 400°F. Rub the cut side of each half with olive oil, then sprinkle with salt and pepper. Place the halves cut side down on a baking sheet lined with parchment paper.
Cook for 30 to 45 minutes, until the skin is softened. Cooking time will depend on the size of the squash. Remove from oven, and carefully flip over each half using a dish towel or oven mitt. Use a fork to loosen the spaghetti squash noodles. Enjoy!
If you don't have a microwave, you can still cut spaghetti squash in half, but it will take some extra elbow grease and more time. Start by slicing off the stem, then carefully cut the squash in half lengthwise, pausing as needed. Making slits in the skin along the line where you will cut before making the bigger cut may help.
You can also cook a spaghetti squash entirely in the microwave if you don't want to use the oven. Start by following the instructions for making slits in the spaghetti squash and softening the skin in the microwave (the first two steps above). Then, cut the squash in half, remove the seeds, and place the halves cut side down in a casserole dish with ¼ cup water. Cook for 5 to 10 more minutes in the microwave until the skin is softened and can be pierced with a fork.
Store cooked spaghetti squash in the fridge for up to a week.