Put cranberry sauce in a medium mixing bowl. Break up sauce with a fork. Set aside. Put cold water in a small saucepan. Sprinkle gelatin over cold water; let stand 1 minute or until gelatin is moist. Cook over low heat until gelatin is completely dissolved, stirring frequently. Add gelatin to cranberry sauce. Cool slightly. Add ginger ale and lemon juice. Chill in refrigerator until mixture begins to set. Stir in apple, celery and walnuts. Spoon into 6 individual molds or a 1-quart mold. Chill until firm. Unmold and serve on lettuce, with mayonnaise. Makes 6 servings.