Use a bbq with a lid. Light and place the coals either side or around the edge of the bbq but not under it. Put a foil dish, either homemade or bought in the middle with some water in it. Fat drips will burn and ruin the meat. Place the joint in the middle and leave it to cook. It should cook faster than an oven and it will be moist and tasty. For an improved flavour put water soaked fruit or oak chips over the coals.