Put the boiled potatoes into a mixing bowl and mash with a masher. Finely chop the green chilli and add to the potatoes. Add coriander leaves, ½ tsp red chilli powder, coriander powder, asafoetida, salt and chaat masala.
Dry roast fennel seeds in a small non-stick pan till fragrant, put them on the worktop and make a coarse powder with a rolling pin. Add this to the potato mixture and mix everything well.
Take gram flour in another mixing bowl, add salt and 1 tsp red chilli powder and mix well. Add sufficient water and mix well with your hand. Whisk thoroughly to make a smooth and thick batter.
Slit the green chillies without cutting through and remove the seeds and pith.
Heat sufficient oil in a kadai.
Stuff all the chillies generously with the potato mixture. Dip them, one by one, into the gram flour batter and slide in to the hot oil and deep-fry on medium heat till golden. Drain on absorbent paper.
Arrange them on a serving platter and serve hot with a bowl of green chutney.