Preheat oven to 160°C. Heat oil in a frying pan over medium-high heat. Cook lamb for 5 mins or until browned all over. Transfer to a plate. Combine sesame seeds, thyme, oregano, lemon zest and salt on a plate. Roll lamb in spice mixture to coat.
Arrange onion in a medium roasting pan. Place lamb on onion. Pour stock into the roasting pan. Cover tightly with foil and roast, adding extra stock if required, for 2¼ hours or until lamb shreds easily with a fork. Set aside for 15 mins to rest. Shred lamb with a fork.
Combine yoghurt and lemon juice in a bowl. Spread pita with hummus. Top with eggplant, cucumber, shredded lamb, mint and tomato. Drizzle with lemon yoghurt and roll up to eat.