Heat the oven to 180°C (350°F/Gas 4). Blitz the chickpeas in a food processor to a paste. Transfer to a mixing bowl and add the flour, salt, flax egg, ras el hanout and the olive oil. Mix well, then gradually add about 70 ml (2¼ fl oz) water – use just enough to form a dough that will roll out without crumbling. Knead for a minute or so. Shape into a disc, put between 2 sheets of baking paper and roll out to a thickness of 4 mm. Peel back the top layer of paper and stamp out 5 cm (2 inch) circles with a cookie cutter. Transfer to a baking tray lined with baking paper. Brush with olive oil and sprinkle with the nigella seeds (if using), gently pressing them into the dough.
Bake for about 15 minutes, or until firm and pale gold. Transfer to a wire rack to cool.
Meanwhile, to make the tapenade, put the peppers, garlic, capers, chopped coriander and the extra virgin olive oil in a food processor. Blitz to a rough sauce. Season with salt and pepper.
To serve, spoon 1 teaspoon of the tapenade onto each chickpea bite and top with a coriander sprig.