Prick the leg of mutton with a fork and mix all of the ingredients (except the oil) and leave it to marinade for about 1 ½ hours.
Put the leg in a big pot and cover. Let it cook until all of the juice dries up.
Add the oil to it and in case it is not tender, add half a cup of warm water and leave it covered for a while until it is done.
Serve it on a plate or dish garnished with lettuce and cucumber, spoon the remaining sauce from the pot and add on top of the roast.