Separate endive leaves; trim off and discard hard white ends.
Put in cold water, and let stand to reduce characteristic bitter taste.
Place orange and onion slices in bowl, and pour over enough dressing to cover.
Chill in refrigerator.
Just before serving time, drain and dry endive, and arrange on individual plates.
For each serving arrange 2 or 3 orange slices with 1 onion slice on endive; surround with 1/2 slices of avocado dipped in dressing.