Grind together coconut and cumin with 1/4 cup water to a smooth paste. Add ground coconut to buttermilk or whisked yogurt and mix well.
Peel the skin and remove the seeds from vellarikka and cut into bite size pieces. Cook together vellarikka, green chilli, turmeric powder with salt and 1 cup water. Cook till the vellarikka becomes tender and water is almost dried.
Add coconut buttermilk / yogurt mixture to cooked vellarikka and mix well. Stir continuously until the steam comes through the spatula. Dont let it boil. It will take around 5-7 minutes. After removing from gas, stir for a few more minutes.
In another pan, heat oil and crackle the mustard and fenugreek seeds, add dried red chilli, sliced small onion and curry leaves. Fry till the onion turns golden brown. Add this to the vellarikka moru curry and mix well.
Serve hot with rice.