Place the chicken, avocado, apple, celery, and red onion in a medium bowl. Gently mash the avocado with a fork and stir it around so that everything gets well mixed.Add the cilantro or parsley, lime juice or lemon juice, salt, and pepper. Add more lime juice or salt to taste. If the mixture seems a little dry, you can stir in a teaspoon or two of olive oil.To store, place in a bowl and cover completely with plastic wrap so that no part of the chicken salad is exposed to air. Will keep a couple of days in the fridge.