Cut avocados in half lengthwise, remove pits, but do not peel. Combine tuna, celery, chives, Italian dressing, and mayonnaise. Mix well. Spoon into avocado halves and arrange on shallow baking dish. Pour half inche boiling water into the bottom of dish. Sprinkle tops of avocados with cheese. Bake at 200ºC for approximately 15 minutes. Before serving, sprinkle with the crushed potato chips.