Heat the oil in a large saucepan, then add the cumin seeds. Once they start to sizzle, add the onion and cook for 8-10 minutes until golden brown. Add the ginger and garlic and cook for 1 minute more.
Add the chopped tomatoes, then cover and cook for 10 minutes on low-medium. Add the salt, the spices and 100ml just-boiled water, then add the chickpeas and coriander
Preheat the oven to 200ºC, gas mark 6. Transfer the chickpeas to a large ceramic pie dish and allow to cool. Brush the rim of the dish with a little egg. Unroll the puff pastry sheet on top to cover the dish. Trim away any excess pastry, press down a little on the rim, then crimp the edges. Keep any trimmings in the fridge for another recipe.
Brush the pastry with more egg, cut a cross in the middle to let out steam, then bake for 25-30 minutes until crisp and golden. Serve hot, with yogurt and a leaf salad, if liked.
