Beat curd well in a mixer. Grind coconut and cumin together in the mixer.
To a a pan, add yams and plantain, turmeic powder, chili powder, water and salt and let cook. Now transfer curd to the pan and simmer the flame. Keep stirring until the mixture thickens and the quantity is reduced by half. Now add coconut cumin mixture and keep stirring for another 5 minutes. Turn off the flame and transfer it to a serving bowl.
In a frying pan, heat oil. Add mustard and let splutter. Now add pepper, fenugreek, red chili and curry leaves. Give a few strokes and transfer it to the bowl and stir it well into kaalan.