Clean and wash the fish slices and rub turmeric all over them. Marinate for 15 minutes
Dry roast grated coconut in a frying pan over medium heat. Add coconut oil on the other side and allow to heat for 10-15 seconds. Add onion and sauté for 2-3 minutes
Add dry red chillies and roast for another minute while stirring occasionally. Remove the mix from the pan and set aside to cool.
In the same pan, dry roast mustard seeds, coriander seeds, garlic cloves, curry leaves, tamarind and black peppercorn for 2-3 minutes or until fragrant
Add both the roast mixes to a food processor or blender along with chopped tomatoes and water. Blend to a smooth thick paste
Heat coconut oil. Once the oil is hot, add the ground paste and mix
Add salt, red chilli powder and stir to combine. Bring to a boil, lower the heat and simmer for 10 minutes
Slide the fish into the pan and mix gently so as not to break the fish
Simmer over medium heat for 10-12 minutes
For the tempering, heat oil, then add garlic and fry for 1 -2 minutes. Add mustard seeds and curry leaves