You can use a bone in leg of lamb and just cut slits in the meat and smear in some harissa and then cover the leg all over with more harissa and Ras el Hanout. Your cooking time will vary of course.
The chermoula sauce that was used to marinate the
Herb Grilled Chicken goes wonderfully with this lamb as well.
I used the last of my homemade harissa on this lamb and bought some extra from Whole Foods, which is quite excellent. You can either make your own or buy a jar.