Boil the vegetables in 1 cup water with salt, turmeric powder, and chilli powder till tender.
Grind the coconut and curd into a smooth paste. Add to the boiled vegetables. Bring to a quick boil for just a few seconds.
For tadka, heat oil in a frying pan. Add the first 3 tadka ingredients and fry till seeds start cracking. Add curry leaves. Pour the mixture to the aviyal and serve.