Rub the lamb cutlets with 1 tbsp oil and 1 tbsp sumac and cover. Refrigerate for 30 mins or up to overnight.
Grill, toast or bake the bread until lightly browned and crispy. Break into shards with your hands.
Preheat a large chargrill over a moderately high heat. Season the cutlets with salt and pepper and grill for 3-4 minutes on each side or until cooked to your liking. Cover and set aside to rest for 5 minutes.
Meanwhile, place the tomato, cucumber, capsicum, onion, radish and herbs into a bowl and add the lemon juice and remaining olive oil. Season with salt and pepper and stir to combine. Transfer to a salad bowl and top with the bread shards and remaining sumac. Serve at once with the rested cutlets.