Mix the flour and salt together in a bowl, then add enough water to bring the mixture together into a dough – about 7–8 tablespoons. Turn out on to a lightly floured surface and knead well until smooth. Return to the bowl, cover with clingfilm and leave in a warm place for 30 minutes.
Toss the peppers and onion with the oil in a large roasting tin, then add the coriander and cumin and toss again. Roast in a preheated oven, 220°C (425°F), Gas Mark 7, for 20 minutes until softened.
Meanwhile, blend together all the ingredients for the hummus in a blender or food processor until smooth.
Divide the flatbread dough into 4 pieces and roll out each into a 25 cm (10 inch) round. Heat a large frying pan until hot and cook the flatbreads for about 45 seconds on each side until lightly golden, flipping over with a fish slice.
Spread each warm flatbread with some of the hummus, then top with one-quarter of the hot roasted vegetables and fold to serve.