Place the chickpeas in a food processor with the tahini paste and whiz until thick. Add the lemon rind and juice, olive oil, chives and measured water. Whiz again until smooth and creamy.
Toss the carrots, cucumber and cress in a bowl.
Lightly toast the pitta breads for 1 minute in a toaster until warm and slightly 'puffed'. Halve each pitta and fill, while warm, with the hummus and salad. Serve straight away.