Cut fish into large cubes. Place in a glass bowl with ground turmeric, lime juice and salt. Mix well. Cover with cling film and marinate in the fridge for 30 minutes.
Heat oil in a heavy-bottomed cooking pot on high. Add cinnamon, mustard, cumin, fenugreek, fennel, lemongrass and curry leaves. Sauté for a few seconds until the spices are fragrant and start to crackle and pop.
Reduce heat to medium. Add onion and green chilli. Cook for 6-8 minutes until onion softens.
Add garlic. Sauté for a few seconds until golden.
Add black pepper, salt, cardamom, ground coriander and tomatoes. Cook for 5-6 minutes, stirring occasionally until tomatoes have softened and are starting to caramelize.
Add tamarind paste and coconut milk. Check for seasoning and adjust salt if necessary. Reduce heat to medium-low, cover and simmer for 8 minutes.
Add marinated fish and pandan leaf (if using). Cover and simmer on medium-low for another 5-6 minutes until fish is cooked through. Remove from heat, garnish with coriander leaves and serve hot with steamed rice.
Notes
Fish - This milder, yellow Sri Lankan Curry is always made with a firm white fish. My favourite is Barramundi. But I also love using Cod or Tilapia in my curries. Tilapia is wonderful as it is very low in mercury due to its fast-growing nature and has a delicious flavour. You can also substitute with Basa, Snapper, Halibut, Ling or Mahi Mahi. Lemongrass - I like to use fresh lemongrass when I can find it or harvest it in my veggie patch. When I don't have fresh lemongrass on hand, I use lemongrass powder (about 1/2 teaspoon for this recipe). This is very handy to have in your pantry, lasts for months and is perfect for giving that tangy flavour in Asian dishes. You can usually buy it at spice stores.Tamarind paste - It is a South Asian paste made from tamarind pulp. It is smooth, thick and brown. It has a very sour flavour and should be used sparingly. It can be found at Asian supermarkets or Asian aisles at regular supermarkets. If you can't find it, substitute with 2 tablespoons lime juice.Pandan leaf - Pandan leaf is thin and dark green like a fat blade of grass. It is deeply fragrant and often used to flavour Asian steamed rice, curries and desserts. Fresh and frozen leaves can be found at specialty grocers or frozen section of Asian supermarkets. Fresh leaves barely last 2 days before turning brown. Frozen leaves last for years and are great to have in the freezer. If you don't have pandan leaves, just leave them out.