The best cut for this is a boneless rump of lamb as it's always tender and is a nice compact cut to slice when it's cold.
1 rump of lamb, off the bone and fat removed
A little vegetable or corn oil
Salt and freshly ground black pepper
Half a cucumber
20 or so mint leaves
Preheat the oven to 200C/gas mark 6. Season the lamb, heat a little oil in a frying pan and brown the lamb on all sides then transfer to the oven and cook for about 7-8 minutes, keeping the meat nice and rare, then remove from the oven and leave to cool.
Meanwhile cut the cucumber into 3-4cm lengths, or 1cm or so longer than the depth of the lamb so that when they are wrapped you will still be able to see the cucumber.
Stand the cucumber upright and cut down into four pieces around the seeds. Cut the pieces into fairly regular batons and put to one side.
Slice the lamb as thinly as possible and lay the slices on a chopping board. Lay about 3 or 4 batons on each slice of lamb with one or two mint leaves and roll them up. You can serve these as they are, or with a little blob of mint sauce or jelly if you wish.