Preheat oven to 400 degrees. Place squash quarters cut side up in square baking dish. Add 1/2 cup water. Bake, covered, for 30-40 minutes or until squash is tender when pierced with a fork.
Meanwhile, spray a medium skillet with cooking spray; place over medium heat. Add apples, raisins and walnuts. Cook for 5 minutes or until apple slices are tender. Set aside.
For maple syrup, combine apple juice and cornstarch in a small pan. Bring to boil over medium heat, stirring constantly. Boil and stir until thickened and bubbly (it should coat the back of a spoon). Remove from heat. Stir in butter, sweetener, maple flavoring and vanilla until well blended.
Add maple flavored syrup to apple mixture. Cook 2-3 more minutes or until heated through.
As squash comes out of oven, place squash on serving platter and spoon apple mixture over top of squash.