1. In a kadai, heat 2 tbsp of coconut oil. add 1 tsp of mustard seeds and let it splutter.
2. Add 1 large onion, 4-5 garlic cloves, a piece of ginger, 2 green chillies slit, and few curry leaves. saute the onions till they are golden brown in color.
3. Add 2 tomatoes and saute. add 1 tsp of rock salt, 1/4 tsp of turmeric powder, 1 tsp of red chilli powder, 1 tsp of coriander powder, 1 tsp of cumin powder and mix well.
4. Add 1/2 cup of water and mix well.
5. Add the cleaned fish pieces. close and cook the fish pieces for 10 minutes.
6. Flip the fish pieces and let it cook for about 2 minutes. reduce the flame to a low and add 2 cups of thick coconut milk.
7. Mix the curry gently so as to not break the fish pieces. check for seasoning and add required salt and mix gently.
8. Add a sprig of curry leaves and close and cook for 5 minutes on low flame.
9. The coconut milk fish curry is ready to be served.