Heat coconut oil in a small pan and splutter mustard seeds. Then add chopped shallots, crushed ginger and garlic. Saute until light brown in colour.
Add sliced tomato and green chilly and saute for 5-10 minutes.
Take a bowl and add all powdered masalas(red chilly powder, turmeric powder), salt and required water. Mix well and keep it aside.
Pour the masala mixture into the hot pan and keep stirring till the gravy becomes thick and oil appears on top. It will take around 10-15 minutes on medium flame.
Add fish and cook till the fish is done.
Grind grated coconut, shallots and fennel seeds with little water to make a smooth and fine paste. Then add the ground paste and into the pan and pour little water only if required to get the correct consistency.
For tempering heat oil in a pan and splutter mustard seed. Then add chopped shallots and curry leaves. Saute till the shallots turn light brown in colour. Turn off the flame and add 1/2 tsp red chilly powder and mix well.
Pour into the curry and mix well Serve it with steamed rice ,chappathi etc.