Kappa /tapioca with fish and ulli chammanthi /shallots chutney is a delicious dish which I usually crave for... :) This fish preparation is not a curry , it is the "mathi thappuvechathu" dish which we do prepare using the old baking method! (See the recipe and baking method here)
During a specific season, we get fresh big sardines (mathi / chaala) which contains lots of fat ( meen neyyu) in it and with the lesser number of bones too. That kind of sardines are good for preparing this. Sardines soak in the thick masala of freshly ground ginger, garlic, shallots, pepper, gooseberry (or tamarind) etc and slowly reduce water on a medium heat.You can try this with ayala/mackerel also.
For preparing Kappa / tapioca,
Cut and peel the roots. Wash and boil in water enough to soak it. Add salt when it is boiled. Cook and drain when it is done.
I have posted a Ulli chammanthi recipe before, with dry red chillies. This one is with green chillies, which is best with kappa.
Small onions 7
Tamarind 1 gooseberry size
Green chillies 4 (according to taste)
Peel small onions, wash them.. Grind all the ingredients together and add coconut oil in the end.
See other Kappa / Tapioca preparations here.