Discard the outer portion of the yam and banana. cut into small pieces and cook well with turmeric, and salt. Grind the coconut with cumin seeds well, and crush the green chillies with them. Mix with the curd and add this into the cooked vegetables. When it starts boiling keep out of the fire and fry mustard seeds, fenugreek seeds, red chillies and curry leaves in oil and mix with the curry