1.Preheat oven to 180°C (160°C fan-forced).
2.Line two large oven trays with baking paper.
3.Split bread in half to form thin rounds; cut each round into quarters. Arrange on trays, in a single layer. Spray both sides lightly with oil; sprinkle with sumac.
4.Bake for about 10 minutes, or until golden and crisp. Cool.
5.Meanwhile, blend or process remaining ingredients until finely chopped. Season to taste.
6.Serve tapenade with crisps.
The tapenade can be made 3 days ahead; keep refrigerated. The pitta crisps can be made a day ahead; store in an airtight container.Note