1. Prick the leg of mutton with a fork and mix all the ingredients (except for oil) and leave it to marinate for about 1 1/2 hour.
2. Put the leg in a big pot and cover. Let it cook till all the juice dries up.
3. 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 till it is done.
4. Serve it on a plate or dish garnished with lettuce and cucumber, spoon the remaining sauce from the pot on top of the roast.