Preheat oven to 375 degrees. Spray two rimmed baking sheets with cooking spray or oil and place squash rings on sheets.
Cook quinoa in broth according to package directions. Cool slightly.
Heat olive oil in a medium skillet over medium heat. Add onion. Cook about 10 minutes, or until onion is just beginning to brown. Add apple and cook about 5 minutes more, until apple is softened. Allow to cool slightly.
Combine quinoa, apple and onion mixture, cheese, cranberries, sage, and walnuts in a large bowl. Add salt and pepper to taste. Stir in egg.
In a small bowl, combine butter and maple syrup. Brush tops and insides of squash rings with butter mixture; season with salt and pepper.
Stuff quinoa filling into the center of each squash ring, pressing down to fit as much stuffing as possible without overflowing. Spray centers of squash rings with oil or cooking spray. Bake 30-40 minutes, or until tops are golden brown and squash is tender.