Dry roast the rice and dal on medium heat for four to five minutes. Cool and grind into a semi-coarse powder. Put the powder in a bowl. Add yogurt and one and a half cups of warm water.
Mix thoroughly so that no lumps are formed and the batter is of pouring consistency. Add salt and let it ferment for eight to ten hours. Grind ginger and green chillies to a paste.
Once the batter is fermented, mix in the ginger-green chilli paste. Grease the dhokla platter or a thali. Boil water in the steamer/boiler.
Pour half of the batter in another vessel. In a small bowl, add one-fourth teaspoon of soda bi-carbonate, half a teaspoon of oil and half a teaspoon of lemon juice.
Add this to the batter and mix well. Repeat this for the remaining batter just before putting it in the steamer. Pour this onto the greased platter and steam it in the steamer for eight to ten minutes.
Check by inserting a knife. If the knife comes out clean, it is cooked. Sprinkle finely chopped coriander leaves and serve hot with green chutney.