Preheat the oven to 180°C.
Bake pollack with butter on a tray for 10-15 minutes and leave to cool.
Flake the cooled fish fillets.
Blanch prawns in boiling salted water for 30 seconds, cool, and chop into pieces.
Boil potatoes until tender, drain well, and mash.
Mix pollack, prawns, mash, onions, chillies, fish sauce, lime, curry powder, and herbs in a bowl.
Shape into fishcakes and chill in the refrigerator for 30 minutes.
Shallow-fry fishcakes in hot vegetable oil for 4-5 minutes per side until golden.
Combine all salsa ingredients in a separate bowl.
Serve the fishcakes with the pineapple salsa and a drizzle of chilli sauce.