There's no question standing rib roast and whole roasted sirloin (and their porcine counterparts) are show-stopping party pieces when you're having a barbecue. My favourite, though, is a little out of the box: the lamb leg. I use my Big Green Egg barbecue whenever I can; lamb always works with smoke and fire. The classic roast is what most people think of first when you're talking about the leg, but it can be brilliantly cooked over charcoal.
Ask your butcher to bone and butterfly the leg (if you're handy with a knife you can do it yourself). It should all be one thickness to ensure it cooks at the same rate, and will open out to about the size of an A3 piece of paper. Marinate it overnight in all the classic lamb-friendly aromatics: garlic, rosemary, salt, oil.
When your mates turn up, heat the barbie to high and cook it for half an hour. What you're after is that contrast of charred, crisp, caramelised bits and juicy pink flesh. Give it time to rest, and serve it chopped up in rough pieces on a big platter with roast potatoes, seasonal vegetables and maybe some gremolata.