Mix ingredients for marinade in a small bowl. Make spiral cuts on the duck breasts. Brush half of the marinade over them, gently separating the meat slices so that it reaches the middle of the breast meat. Set aside to marinate for about 30 minutes.
Preheat oven to 180 deg C. Place the marinated duck breasts skin side up in a roasting pan and cover loosely with foil.
Bake for about 15 minutes, occasionally basting the meat with remaining marinade. Bake for another 15 to 20 minutes to finish cooking. Serve with pan drippings and a vegetable salad.