Heat the oil in a pan, add mustard seeds, curry leaves and channa dhal, then add broken cashew nuts, switch off the flame, keep the pan in that heat; add the bulgur wheat and stir well. Remove the mixture from the pan and pour it in a large bowl.
15 minutes before making idli, take the bulgur wheat mixture, add bicarbonate of soda and yogurt mix it well.
At this stage add grated broccoli, the mixture should be like a batter. Add some more yogurt and water until it reaches to the consistency of rava idli mixture or a thick batter.
Grease the idli moulds, pour spoonful of mixture into the idli plate. Steam it in the pressure cooker or rice cooker. (These idlis take a slightly longer time to cook than the normal idlis. Check the idlis with a skewer if it's cooked.) Once the idli looks firm on top, remove from the cooker and leave the idlis in the idli plate for 15 minutes to rest.
Then carefully remove the idlies form the mould with a spoon gently without breaking. These idles are best after 30 minutes.
Serve the idlies with sambar, fish or lamb gravy, and chutney.