Start by making the puri dough – mix the flour and salt with 125ml of warm water and bring together to make a dough. Cover with cling film and chill for 20 minutes.
Meanwhile, dry fry the cumin seeds and coriander seeds for 1-2 minutes, until you can smell the spicy aroma.
Pour the seeds into a pestle and mortar and gently grind them, to break them down and release their flavours. Stir in the remaining spices.
Heat the oil in a pan and cook the onion and green chillies for 1 -2 minutes before stirring in the ginger and garlic pastes and cooking for a further 3-4 minutes.
Stir the spices into the pan and cook for a minute.
Add the chopped tomatoes and chickpeas and 200 ml water. Bring to a simmer, and then cook for 20 minutes.
Meanwhile, divide the puri dough into small balls and roll each one to a 7-8 cm circle.
Heat the vegetable oil in a deep heavy-based saucepan until hot – when you drop a small piece of the dough into the oil it should sizzle. Deep-fry each puri for 45 seconds, turning once. Remove with a slotted spoon and drain on kitchen paper.
Stir the lime juice and coriander into the chana masala and serve with the puri.