Lamb leg is a lot leaner and meatier than the shoulder, so you get more meat for your money. No bones makes it a much easy to carve roast which is also a great option if you would like to add your own stuffing.
Preheat conventional oven to 250C/475F. Gas Sear meat for 15 minutes in oven. Then 15 minutes per 454g (1lbs) of meat. Leave meat to rest for 30 minutes before carving.