Soak the chickpeas overnight in cold water at least twice the volume of the chickpeas.
The next day, drain the chickpeas and place in a food processor with the onion, garlic, herbs, spices, salt and egg.
Pulse the mixture until just finely chopped and combined (not mushy or pasty).
Add the baking powder and chickpea flour and mix until combined.
Place in the fridge for at least an hour.
While the mixture chills make the white bean yoghurt by placing all the ingredients in the food processor and pulse until well combined.
Heat the oil in a medium sized saucepan (to reach at least 5cm up the sides of the pan) and test if the oil is hot enough by dropping a small bit of mixture into the oil. The mixture must start to sizzle and fry immediately.
Wet your hands and press the mixture into balls about the size of a walnut.
Fry in the oil in batches for 6 - 8 minutes until well browned and cooked through.
Drain and serve while hot in a wrap or pita with the chopped tomato, parsley, sesame seeds and the white bean yoghurt.
Adapted from Roger Jorgensen and Ottolenghi