Go with roast. Stud it with garlic, rosemary and anchovies, roast on a trivet of veg (celery, carrot, onion, bay leaves, peppercorns, or whatever you have lying around). There won't be much fat coming off a leg, but was does will caramelise the veg underneath. When the meat is resting, adding boiling stock to the roasting pan will give the base for a wonderful gravy. Mash in the veg, strain, reduce, add red wine, reduce, thicken = stunning gravy.
Lamb gives off a lot of water and fat when cooked
I'm not familiar with how lamb is produced in the US, but over here it doesn't yield much water. Fat, yes from some cuts, but not the leg, which is very lean, and is well suited to cooking medium rare.
In the UK, we separate the lower part of the leg (the shank), which is a little fattier. This part I would always casserole/slow cook on a low heat (6+ hours) until the meat falls off the bone. This also produces excellent gravy.