Dry roast the gingelly seeds, cumin seeds and timmur in a pan. Grind together with a little water.
Transfer the potatoes to a serving dish, add the ground spices, salt and lemon juice and mix well.
In a pan, heat the oil and add the fenugreek seeds to it. When they crackle, add the green chillies and cover for a minute. Add turmeric powder and pour the tempering over the potatoes. Mix well, garnish with coriander and serve cold.