Preheat oven to 400°. Cut squash in half lengthwise and scoop out seeds. Place halves in a large baking dish, cut side up; add 1/4 inch of water to pan and cover with foil. Place in oven and bake for 45-50 minutes, or until tender. Remove from oven.
Using oven mitts to hold squash, scoop out pulp, transfer to a medium bowl, and mash. Stir in goji berries, maple syrup, walnuts, cinnamon, and salt to taste. Serve immediately.