Prepare the dressing by placing all the ingredients in a plastic container with a tight fitting lid and shake.
To cook the chicken, bring a large pot of salted water to the boil, plunge the breasts in, then immediately remove pot from the heat and allow the water to cool (takes about 1 hour). Remove the breasts. They should shred easily.
Place the leaves in a stainless-steel bowl and dress with a third of the dressing. Divide leaves between 4 plates.
Add the chicken, chives, parsley, salt and freshly ground pepper to the bowl and dress with enough dressing to coat well (about 100ml), then divide between plates.
Add avocado to the bowl and dress with a tablespoon of dressing. Sprinkle the avocado over the plates, then serve.