Heat the oil in a large frying pan and add the ground coriander, cumin seeds, tomatoes and shallots. Stir-fry for 2 minutes, then add the chilli powder, turmeric, dhana-jeera, sugar and lemon juice to taste. Stir to mix well.
Add the potatoes and water, cover and cook gently for 10–15 minutes or until the potatoes are tender. Stir in the fresh coriander, season with salt and pepper and serve hot with pappadoms.