Preheat oven to Gas 6, 200ºC, fan180ºC. Cut the peppers in half and remove cores, seeds and stalk. Roast for 15-20 minutes until the peppers have blistered. Put in a plastic food bag, seal and cool for 15 minutes.
Peel away the skin and place in a food processor with the drained chickpeas (reserve some chickpeas and a strip of red pepper to garnish the dip), garlic, cayenne and lemon juice. Whizz to a purée. Add the yogurt and again whizz briefly. Season to taste.
Garnish the dip with the reserved chickpeas and red pepper and a sprinkling of cayenne pepper.
Cut pitta breads into triangles and bake for 5 minutes until crisp. Serve warm with the dip and crudités.