Ask your butcher to bone the lamb for you, opening it out flat, or butterfly the lamb so that it is flat and of a uniform thickness. Place the lamb in a non-metallic dish. Score the skin criss-cross ways. Pour over the teriyaki sauce and honey, cover and refrigerate. Allow to marinate for up to 24 hours, turning occasionally. If you forget, don’t worry. It’s nice with just a few hours.
Preheat the oven to 250ºC/475ºF/Gas 9. Lay the lamb skin-side up in an oiled roasting tin. Pour over the marinade. Roast for 25-30 minutes, and then leave to stand for 20 minutes covered with tinfoil and a tea towel before slicing and serving. If necessary stir the teriyaki sauce into the roasting dish and reheat (I don’t think this is necessary but add lamb juices). Garnish with coriander and serve.