To make the dressing, mix all the ingredients together in a small pot and bring to the boil. Remove from the heat and leave to cool or refigerate.
Remove the chicken from the bones and slice thickly across the grain. Put the chicken, onion and tomato in a bowl, drizzle with the dressing and gently toss together. Put the lettuce on a serving plate and arrange the chicken salad on top. Sprinkle with peanuts to serve.
Variation: This is a salad where you can interchange chicken for duck, beef, lamb, quail or even prawns to create a lively, fresh tasting dish.