½tablespoons pickled pink peppercorns, drained and rinsed
1tablespoon snipped chives
rocket (arugula) leaves, to serve
Put the chicken between two sheets of plastic wrap and pound each with a mallet or rolling pin until 1.5cm (⅝inch) thick. Put 2tablespoons of the oil in a shallow dish with the vinegar, and season with salt and pepper. Toss in the chicken, then cover and marinate in the refrigerator for 15 minutes, turning once.
Preheat a barbecue grill and brush with oil. Drain the chicken and cook for 7–8 minutes, or until cooked through, turning once. Remove from the heat, cool to room temperature, then slice.
Peel the grapefruit, removing all the bitter white pith. Working over a bowl to catch the juices, cut the grapefruit into segments between the membrane, removing any seeds. Reserve a tablespoon of the juice and whisk in the mustard and remaining oil to make a dressing. Add the peppercorns and chives and season with salt and pepper to taste.
Arrange the rocket on four plates and top with the chicken and grapefruit. Drizzle with the dressing and serve.