Preheat the oven to 450 degrees F.
Split the squashes in half and scrape out seeds. Line an oven tray with aluminum foil. Season the spaghetti squash with olive oil, salt, and pepper. Place flesh side down and roast for 30 to 40 minutes until fully cooked. Remove from the oven and let rest until cool enough to handle.
Meanwhile heat the marinara sauce in a large saute pan.
When squash is cool enough to handle, using a large kitchen spoon scrape the strands of squash from the inside of the skin. Toss the spaghetti squash in the pan with the hot marinara for just long enough to get hot. Serve and enjoy.