Take a wok, add oil and heat it.
Add cumin seeds, mustard seeds and allow them to splutter.
Add dried red chillies, fresh curry leaves and let the leaves crackle.
Add in the finely chopped onions and saute then until they turn slight brown in color.
Add ginger garlic paste and saute for few seconds.
Add the finely chopped tomatoes.
Add dry spices such as salt, turmeric powder and red chilli powder.
Mix everything and let the tomatoes cook until they turn soft.
Add the coconut milk or the thin coconut blended paste.
Let it cook for 5-10 minutes.
Add about 1 cup of tamarind extracted pulp.
Add the main spices such as coriander powder, cumin powder and black pepper powder.
Add some fresh curry leaves, check for salt and if required.
Let the curry boil for 5-10 minutes.
Add the tomato which is cut into four halves into the curry for flavor.
Add in the marinated fish pieces.
Give a stir delicately.
Add in some freshly chopped coriander leaves.
Let the whole gravy cook for 10 to 12 minutes along with fish.
Switch off the flame.
Serve hot with rice.