Cook the spaghetti squash. Preheat oven to 375 degrees F. Prick the squash all over with the tines of a fork. Place on a baking sheet, and put the squash on its side in the preheated oven. Bake for about 1 hour, or until soft to the touch. Turn once mid-baking. Remove from the oven. Let cool for about 10 minutes before slicing. Slice it horizontally, and scoop out the seeds and pulp. With a fork, scrape the squash into a large bowl and let cool completely.Add the salad dressing, salt, pepper flakes, bell pepper and scallion. Toss gently to combine and coat the mixture with the dressing. Taste and add more salt and/or red pepper flakes if desired.Serve at room temperature or transfer to an airtight container and refrigerate until chilled, at least 2 hours.