Heat the oil in a large pan and add the mustard seeds, curry leaves and onion and allow to splutter. As soon as the onions soften (not brown) add the ginger, garlic, turmeric and salt and cook for 30 seconds.
Add the tomatoes and stir-fry for 1–2 minutes, then add the whole green chillies. Next add the coconut milk, 50ml of water and turn the heat down low. Cover and simmer for 7 minutes.
Remove the lid and add the haddock pieces. Gently cook until the fish is cooked through (about 3–4 minutes), stir through the lemon juice and adjust the seasoning if needed. Serve with plain rice.
