Step 1: Prick the lamb on all sides with a fork the holes should be about 1/2-inch deep. This helps with the absorption of the marinade. Place the lamb in a nonreactive baking pan just large enough to hold it.

Step 2: Make the marinade. Place the soy sauce, lime juice, vegetable oil, water, salt and pepper in a mixing bowl and whisk to mix. Pour this mixture over the lamb, turning the meat to coat on all sides. Marinate the lamb, covered, in the refrigerator for at least 6 hours or as long as overnight, turning several times so it marinates evenly.

Step 3: Drain the lamb, discarding the marinade. Blot the lamb dry with paper towels. If spit-roasting, thread the leg of lamb on a rotisserie spit. If indirect grilling, leave it as is. Brush the lamb on all sides with melted butter and thickly crust with chopped garlic, dried mint, salt, and peppercorns, pressing the ingredients into the meat.

Step 4: Rotisserie method:
Set up your grill for spit-roasting and preheat to medium-high. Spit-roast the lamb until crusty and darkly browned on the outside, about 1 hour for medium-rare. (Use an instant read meat thermometer to test for doneness. Insert it into the deepest part of the leg but not touching the bone. Medium-rare lamb will be about 145 degrees F.) Baste the lamb often with any remaining butter and the drippings.

Indirect grilling method:
Set up your grill for indirect grilling. Place the leg of lamb in the center of the grate over the drip pan, fat side up. Indirect grill the lamb until crusty and darkly browned on the outside, 1 to 1-1/4 hours for medium-rare. (Use an instant read meat thermometer to test for doneness. Insert it into the deepest part of the leg but not touching the bone. Medium-rare lamb will be about 145 degrees.) Baste the lamb often with any remaining butter and the drippings.

Step 5: Transfer the lamb to a platter. Reserve any drippings for the sauce. Loosely tent with foil and let rest for 5 minutes, then carve. Serve with the following Sweet Sour Mint Sauce, if desired.