Take gram flour in a bowl. Add yogurt and warm water and whisk well so that there are no lumps. The mixture should be of a slightly thick consistency. Add salt and leave it covered to ferment for three to four hours. Grind green chillies and ginger into a paste. When gram flour mixture has fermented, add turmeric powder and green chilli-ginger paste.
Adjust seasoning and mix well. Heat the steamer. Grease a dhokla mould or shallow cake tin or a thali. In a small bowl take soda bicarbonate, one teaspoon oil and lemon juice. Mix and add to the gram flour mixture and whisk briskly. Pour batter into the greased thali and place it in the steamer. Cover with the lid and steam for ten to twelve minutes.
When a little cool, cut into squares and keep in a serving bowl/plate. Heat remaining oil in a small pan. Add mustard seeds. When the seeds begin to crackle, remove and pour over the dhoklas. Serve, garnished with coriander leaves and coconut.