Lamb Shashlik with Vinegar-Pickled Onions

Shashlik stands in the Caucasus and Central Asia rarely bother with fancy marinades. Grated onion, salt, pepper and time do the tenderizing, and the real seasoning arrives at the table as sharp vinegar onions. Shoulder is the right cut: it has enough fat to stay juicy over live fire. Cut the pieces generously, around 1 1/2 inches, so the outside chars before the center overcooks, and let the skewers rest on the lavash so the bread catches every drip.