In 8-inch skillet, heat 2 tablespoons of the butter and the walnuts over medium heat, stirring occasionally, until nuts are lightly toasted. With slotted spoon, remove nuts from skillet; place in small dish. Add honey and nutmeg to nuts; mix to glaze. Set aside.
In same skillet, melt remaining 6 tablespoons butter over medium heat. Cook celery and onion in butter over medium heat 3 to 4 minutes, stirring occasionally, until almost tender.
Meanwhile, spray 4- to 6-quart slow cooker with cooking spray. In slow cooker, place stuffing cubes. Add mushrooms and celery mixture; mix lightly. Add applesauce and water; mix lightly.
Cover; cook on Low heat setting 4 to 5 hours.
Just before serving, sprinkle with glazed walnuts.