Heat sufficient oil in a kadai.
Put potato in a bowl, add onions, gram flour, green chillies, ginger, cumin seeds, coriander seeds, fennel seeds, soda bicarbonate, salt, turmeric powder and coriander leaves and mix well. Add one cup water and mix well to make thick mixture.
Drop spoonsful of the mixture into hot oil and deep-fry, stirring occasionally, till three fourth done on all the sides. Drain on absorbent paper.
Break them into smaller pieces and refry in the same oil till crisp and golden. Drain on absorbent paper.
Arrange them on a serving plate and serve hot.