Preheat oven to 375 degrees. Cover a sheet pan with parchment paper, set aside.
With a very sharp knife, slice the spaghetti squash in half lengthwise. Scoop out the seeds and any excess fibers with a spoon.
Rub oil onto the flesh of each squash.
Place squash, flesh side down on the baking sheet.
Roast for 45 minutes or until skin is puckered and flesh is soft.
Remove from oven and set aside until squash is cool enough to handle. With a fork, run the tines through the flesh both vertically and horizontally to break it up and separate the strands.
Transfer to a serving dish and serve with homemade marinara from this site, or your favorite spaghetti sauce.
Notes
I make large batches of marinara sauce (link below) and freeze portions of it in plastic storage bags, so it's always ready to go. Any good spaghetti sauce would work!