If ever there was a summer salad to impress, this would be it. Humble though its ingredients are, they are used in such a way as to make the very most of them. Like many bread salads, this one finds its origins in peasant food but makes a hearty dish humming with spice and flavour. Sprinkle with a little extra sumac before serving for a sharp hit of citrus. You could also replace the sourdough with toasted pitta.