Put the chicken breasts in a large pan and pour over enough cold water to just cover. Roughly chop one of the onions, drop into the pan with the carrot, peppercorns and bay leaves. Cover, bring to the boil, then lower to a gentle simmer for about 35 minutes or until the chicken is cooked. Remove from the heat, but leave the chicken in the liquid to cool down completely. When cold, lift the chicken out of the stock then strain (skim off any fat from the stock) and keep 200ml for the sauce. Can be done a day ahead and chilled. Finely chop the remaining 1/2 onion. Heat oil in a small saucepan, tip in the onion and fry until softened and pale golden for about 5 minutes. Add the curry powder, apricots, tomato ketchup, mango chutney and the reserved chicken stock and cook for a further 5 minutes. Mix together the mayonnaise and Greek yogurt, followed by the cold curry sauce. Season well with salt and pepper. Cut the cooked chicken breasts into thick slices and add to the curried sauce along with the chopped coriander, sliced spring onions and the chopped mango. Mix well together. Scatter the watercress or salad leaves onto a platter, spoon over the Coronation chicken mix and serve.