Cut the idlis into small squares - bite sized pieces. Set aside.
Take a large bowl and add the yogurt. It is very essential that you use non-sour yogurt. If you live in a humid/hot weather where it might get sour soon, you can add in some milk.
Add the spices and salt. You can increase/decrease or add additional spices as per your taste and preferences. The quality and taste of your yogurt might also dictate such changes. So taste as you go. This sauce makes the dish and therefore work on this to your satisfaction before you add the idlis.
Whisk until smooth. You can add in some milk/water if its too thick. Set aside.
Heat a small skillet and add some ghee/oil to prepare the tempering. Once hot, add the mustard seeds. When it pops add the urad dal and curry leaves.
Switch off and towards the end, add some coconut oil, if you like. I don't like to heat the virgin coconut oil too much, hence add it towards the last for a profound coconut flavor. But you can skip this and just use Oil/Ghee.Or you can grind some fresh coconut and mix it along with yogurt. Set aside to cool down a bit.
Add the chopped idlis to the yogurt sauce
and give it to a good toss so that it coats the idlis well.
Garnish with grated carrots
and finally add in the tadka. Combine to mix well.