Preheat oven to 350
Combine first 8 ingredients in a large bowl.
Cut squash in half, scoop out the seeds, place cut side down in a shallow baking dish with a small amount of water, bake for 45- 60 min until squash is tender.
Scoop out flesh of squash from the skin into the bowl with the egg mixture. Mix well.
Spoon mixture into a baking dish sprayed with cooking spray.
Sprinkle marshmallows on top.
Mix together brown sugar, flour, and margarine. Drizzle on top of marshmallows.
Bake for 25-30 minutes until filling is bubbly and marshmallows are slightly browned.