Put the lamb and marinade in a ceramic dish, cover with foil and chill for at least a couple of hours or overnight.
Pat the lamb dry with some kitchen towel and reserve the marinade. Place fat side down your barbecue and cook over medium heat for 10 minutes.
Turn over and brush with the marinade. Cook for another 10 minutes.
Once again, turn the lamb over and brush with the marinade. Cook for a total of 40 minutes, basting with the marinade as you go.
Remove from the heat and leave to rest for 10 minutes. Carve the lamb into slices and serve with chilli jam, sriracha or hot pepper jelly and a big green salad.
<b>To cook on the stovetop</b> Heat a large griddle pan and brush with vegetable oil. Keep the heat medium-high and cook as instructed above, brushing the griddle pan with a little oil if it becomes very sticky. Cooking the lamb in this way can get quite smoky so open a window if you can... or risk the fire alarm going off!