Wash rice and urad dal under running cold water till water runs clear.
Soak them together in enough water for about 5-6 hours.
Drain water well, add it to grinder along with yogurt, ginger and green chilli.
Grind it into a smooth paste. If needed add few tablespoons of water.
Remove it to a bowl, add salt, mix and cover it. Batter should be thick like idli batter.

Let it ferment for 8 hours or overnight in warm place.
Making dhokla recipe:
When you are ready to make dhokla, bring the water to a boil in steamer.
Also grease the pan well with oil. I have used 9 inch cake pan with 1 1/2 inch high side.
Once steamer is ready, add oil into fermented batter, mix.
Add soda, mix well. Immediately pour into prepared pan.
Sprinkle some red chilli powder, black pepper and cumin powder.

Steam it for 10 minutes. Check by inserting a knife or toothpick in it, if it comes out clean and then it is ready.
Let it cool for a minute or two. Then cut into square or diamond shape.
Remove it to plate and serve.