In a medium saucepan, bring the stock to a boil and add the chicken breasts. Boil for 5 minutes, then remove from the heat and place a lid on top of the pan. Leave to sit for 20 minutes, allowing the chicken to cool in the liquid to room temperature.
Julienne the spring onions, then soak in cold water and refrigerate while you make the rest of the salad. This will firm them up and remove the strong onion taste. Quarter or chop the radishes and cut the baby cucumbers into batons.
While the chicken is poaching in the stock, make the Sichuan dressing. Roughly grind the toasted Sichuan peppercorns, then whisk all the ingredients together.
Drain the spring onions and dry on paper towels.
Serve the chicken on a platter or on four plates with the dressing poured over and the radishes, cucumber, spring onions, peanuts, pickled chillies, sesame seeds and fresh coriander scattered over the top.