For the puris, mix the chapatti flour, water, coriander and salt together in a bowl to form a dough. Cover the dough in cling film and chill in the fridge for 20 minutes.
For the spice mix, heat a frying pan over a medium heat. Add the peppercorns, coriander seeds, cumin seeds and cardamom seeds and dry fry for 2-3 minutes or until fragrant.
Transfer them to a mortar and pestle with the other spices and grind to a powder.
For the dhansak, heat the oil in a frying pan over a low heat, add the onion, garlic, chilli and ginger. Fry gently for 12 minutes until the onions have caramelized.
Add the tomatoes and the spice mix and bring to the boil.
Add the lentils and reduce to a simmer for 20 minutes until soft. Then add the potatoes and cook for 10 minutes. Stir in the drained chickpeas to warm through and add lime juice and coriander.
Take the puri dough from the fridge and divide into small balls. Roll each ball out to 5cm/2in discs.
Meanwhile heat the vegetable oil into a deep, heavy-based saucepan until a small cube of bread sizzles and turns golden-brown when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Deep-fry each puri for 1 minute, turning once until puffed up and golden-brown. Remove from the oil with a slotted spoon and drain on kitchen paper.
To serve, place some Greek yoghurt on each serving plate and slide a spoon through it to create a smear. Place two puris on one side of the line of yoghurt, overlapping it slightly. Put a line of curry running down the other side of the yoghurt. Lay two more puris on top of at either end.