For dressing, in a blender container or food processor bowl combine salad dressing and jellied cranberry sauce; cover and blend until smooth. Pour into a small serving bowl; set aside. (Dressing may be made ahead and stored in refrigerator until serving time.)
Squeeze juice from lemon or lime into a medium bowl; add 2 tablespoons water. Add apple slices to juice mixture; turn slices to coat well. Set aside.
In a large serving bowl arrange spinach or watercress and sliced beets. Drain the apples; add to bowl. Serve with dressing. Cover and refrigerate any remaining dressing up to 1 week; stir before using. Makes 8 servings.