Score the duck breasts with a sharp knife in a rough diamond pattern.
Combine the star anise, sumac and peppercorns and rub the spice mixture over the skin. Brush the flesh side of the duck with a little olive oil and set aside for around 30 minutes.
Add the bing cherries to a pan with the water and lime juice and simmer gently for approximately 15 minutes or until the cherries are soft.
Transfer to a food processor and blend until smooth.
Preheat a grill pan to hot. Grill the breast skin side down for 6 minutes before turning over and cooking the other side for a further 2 minutes. Transfer the duck to an ovenproof dish and pour the sauce over the duck.
Place the duck in the oven for a further 5 minutes.
Serve with steamed bok choy.