Combine all the marinade ingredients in a ceramic or glass dish bowl. Pat duck breast dry. Score the duck skin in a crosshatch pattern with a sharp knife (take care not to cut into the flesh).
- Place duck breast into the marinade mixture and turn to coat. Cover tightly and refrigerate for at least 4 hours or overnight. Turn meat at least once during this time.
Bring duck breast to room temperature. Heat a grill or frying pan over a low heat and add the duck breast, skin-side down. Cook 8 minutes until the duck breast is medium-well or until desired doneness. You can sear the duck breast for 3-4 minutes in the pan and then transfer to a 200C/400F oven to finish cooking for 5 minutes. Slice the duck breast and arrange on a platter over a bed of mixed salad. Sprinkle chopped roasted cashew nuts on top.