Cut about 3 inches off the top of the squash and set aside. Cut the squash lengthwise into 4 pieces. (If using smaller squash, cut each squash in half lengthwise). Slice a small sliver off the bottom of each squash piece making a flat surface so the squash will stand upright. Put the rice, spinach, apple, cranberries, optional walnuts, seasoning, sea salt, and ground cinnamon in a medium bowl and stir to combine.