I see that incandescens' father actually uses smoked haddock, which I've never seen up here. Recipe serves 6. One can use less rice if desired.
ETA: eggs, quantum sufficit
12 oz (350 gms) fish
12 oz (355 ml; 1.5 cups) rice
1 green pepper
3 celery sticks
1 small onion
2 tbsp oil
1.5 pints (850 ml; 3.5 cups) stock
2 tsp curry powder
1/4 tsp cayenne
Salt and freshly ground pepper
2 tbsp minced parsley
Hard boil eggs and put to one side. (I used poached eggs, but it's much the same either way)
Wash rice and set aside. (Again, I used basmati which doesn't need washing)
Deseed, core, and chop green pepper. Dice onion and celery fine. Heat oil in a saucepan with a lid, add veg and cook slowly over moderate heat 15 minutes, stirring frequently, until done. Meanwhile heat stock in separate pan.
Add curry and cayenne to veg and cook 2 minutes stirring constantly. Stir in the rice and then slowly add the hot stock. Bring to the boil, stirring constantly. Lower heat, add salt and pepper, cover and simmer 15 minutes until rice is tender but still firm.
(A note here. With basmati the ratio that works for me is 2:1 liquid to rice. This recipe wants a bit more liquid than that, but I'd use whatever ratio works best for the rice you have. And forget the tender but still firm thing. I like my rice soft.)
The recipe then tells you how to poach the fish fillets in milk and water. They call for fresh salmon. With smoked mackerel I just heated it in a little water until warmed through, flaked it, and added it to the rice and veg mix along with the parsley. Adjust the seasoning and transfer to a serving dish oh we are elegant. Cut the eggs in quarters or eighths and use as garnish. Serve immediately.