Rinse and drain the chickpeas, then mash coarsely in a bowl until no whole chickpeas remain.
Finely slice the shallot. Crush the mustard seeds and pepper in a mortar. Heat a tablespoon of oil in a pot and add the mustard seeds. Once they begin to pop, add the shallot and saute for a couple of minutes, until soft. Allow to cool.
Zest and juice the lemon into the chickpeas. Add the cooled shallot mixture and the harissa and blend well with a wooden spoon. Sprinkle over some besan flour and mix with fingers, adding more flour as necessary to make a soft, crumbly dough.
Allow the mixture to stand for twenty minutes in the fridge, then shape into small fritters and shallow-fry over medium heat until golden brown on both sides. Serve in burgers, pita or wraps with salad and your favourite relish.