To make the dressing, place tahini, lemon juice, yoghurt, water and salt in a bowl and stir well. Heat a large non-stick frying pan over high heat. Brush lamb with 1 tablespoon oil and sprinkle with sumac and salt. Cook for 3–4 minutes each side or until cooked to your liking. Remove from pan. Reduce heat to medium. Add remaining oil, eggplant and garlic to pan and cook for 6–8 minutes or until golden and tender. Slice lamb and arrange on plates with eggplant and spinach. Spoon over dressing to serve. Serves 4.