Roast the lamb for about an hour, until it's just starting to go crisp on the outside. Remove from the oven and shred with a fork, then return to oven for 15 to 20 minutes.
Whilst that's cooking peel, cut in half, then slice the cucumber lengthways and do the same with the spring onion.
Remove 4 whole leaves from the lettuce and place in a bowl of iced water and leave in the fridge for about 10 minutes.
Plate up and serve. Place some hot crispy lamb along with the cucumber and spring onion and sauce in each leaf and eat it that way with some fried rice.