Cut small slits in leg of lamb using a sharp knife; insert garlic slices into slits.
Combine vinegar and next 3 ingredients in a large shallow dish or heavy-duty zip-top plastic bag; add lamb. Cover or seal; chill 8 hours or overnight, turning lamb occasionally.
Remove lamb from marinade, discarding marinade.
Sprinkle lamb with salt and pepper.
Grill, covered with grill lid, over high heat (400 to 50
to 45 minutes or until a meat thermometer inserted into thickest portion registers 150 (medium-rare). Cool.
Cut lamb into 1/8-inch-thick slices; serve on Sweet Potato