Rinse the diced fish chunks in water. Drain off the excess water and place the fish in a bowl. Add turmeric powder and a large pinch of salt. Add lime juice and mix. Cover and refrigerate for 25 minutes.
Heat the oil in a deep saucepan over a medium gas flame until seriously hot, but not burning.
Add the chiles, ginger, garlic, onion, and curry leaves to the oil. The curry leaves must be added in at the beginning, so the flavors can infuse with the other ingredients. Stir lightly until onions are transparent. Add 1/2 teaspoon of turmeric powder, and stir. Add enough liquid coconut milk to cover the ingredients in the pan. Do not add the thick coconut milk yet, as it will curdle. Add the fish and a pinch of salt. Bring to the boil, reduce heat, and simmer for 6 to 7 minutes until cooked.
Add the quartered tomato and the thick coconut milk. Garnish with sliced tomatoes and serve with boiled or steamed white rice.