Cook the Basmati rice in boiling salted water with turmeric for 10-12 minutes or until tender. Drain and leave in a colander for a few minutes.
Cut the fish into 4 cm (1. in) pieces and put them in a large saucepan. Pour over the milk and add enough cold water to cover the fish. Bring slowly to the boil, reduce the heat and poach for 3-4 minutes or until the fish is cooked and opaque. Drain away the liquid and set aside.
Melt the butter in a large saucepan or casserole dish and add the curry power, ginger, chillies and spring onion. Stir over a medium heat for 3-4 minutes or until the onions are quite soft.
Add the drained cooked rice and stir together until well mixed. Gently fork in the cooked fish, taking care not to break it up too much. Adjust the seasoning to taste and serve immediately.