Photograph: Tara Fisher
Liberally sprinkle polenta into an oiled 20 x 20cm deep tin to coat the base. Sift the chickpea flour into a bowl. Gradually whisk in 450ml water.
In a large pan, heat the 1½ tablespoons oil over a moderate heat. Fry the cumin seeds briefly; add the turmeric, ginger, chilli, coriander, ¾ teaspoon salt and ¼ teaspoon ground black pepper. Stir for a further minute.
Whisk the chickpea flour mixture once more, then pour into the pan, stirring. Simmer gently for 5 minutes, stirring continuously.
Once the mixture is thick and coming away from the side of the pan, use a spatula to scrape the mixture out into the oiled tin. Quickly wet your hands in a bowl of cold water and flatten the batter out evenly, dipping your hands in and out of the water as needed, until the surface is level. Sprinkle a little more polenta on top, gently press it in and set aside to cool.
To make the tahini lemon dip, mix the tahini paste and lemon juice together with enough water to make a thick dip; season.
Cut the cold chickpea mixture into 24 chips and carefully roll each in a little more polenta. Gently shallow fry in oil, in batches, in a frying pan until crisp and pale golden. Drain on kitchen paper and serve immediately with the tahini lemon dip.
Get ahead: make up to the end of step 4 the day before; chill. The tahini lemon dip can be mixed a few hours ahead.
Kitchen secret: chickpea flour is a delicious naturally gluten-free flour. If you find it hard to get hold of, use 150g polenta instead. Skip the sifting and whisking with water at step 1, and instead add 600ml water to the pan at the end of step 2. Bring to the boil and gradually add the polenta, stirring constantly. Simmer for 5 minutes then continue from step 4.