Chicken Waldorf Salad

One of my favourite scenes from the peerless 'Fawlty Towers' involves an irascible American man, ordering Waldorf Salad.  A baffled Basil Fawlty disappears to the kitchen and re-emerges, declaring that Waldorf Salad is off because they are 'out of waldorfs'.  As well as being very funny, it says a great deal about British food in the 70s!  We are much more comfortable with such exotica now!  As the American angrily barks, the recipe is 'celery, apples, walnuts, grapes - in mayonnaise' and this is pretty much what you do.  I like to cut the richness of the mayo (good old Hellman's) by mixing it with equal quantities of 0% fat Greek Yoghurt and lemon juice to taste - about 2 tablespoons each of mayo and yoghurt and the juice of half a lemon for two people should do it.  I roast chicken breasts for about 20 minutes until cooked but still juicy - season well and drizzle with olive oil before roasting, cool, then cut into chunks and fold through the mayo sauce along with a diced apple, quite finely chopped celery sticks (2), a handful of red grapes, halved, and about 50g of roughly-chopped walnuts, toasted in a dry frying pan.  Pile onto a bed of Batavia lettuce leaves and serve with crusty ciabatta.