1. Beat all the ingredients for the dressing together and season to taste with salt and pepper.
2. Mix the chicken with the olive oil and season with salt and pepper. Heat a heavy-bottomed frying pan until hot and fry the chicken until golden-brown on the first side before turning the pieces over in the pan and browning all over. Once cooked through, allow to cool slightly.
3. Cut or shred the cooked chicken into smaller pieces and mix the salad dressing through; also add any pan juices. Now mix the salad leaves, celery and onion and finally add the creamy chicken. Mix lightly and serve immediately.