Note: snook or sergeant fish isn't available in the UK.It is sometimes called saltwater pike. A top bream bass or even zander would work well.
For the mayonnaise 1 egg yolk
1tsp wasabi powder
20ml rice wine vinegar
100ml warm groundnut oil
50ml stock syrup(1:1 water to sugar)
For the fish 300g skinned snook fillet
4tsp sea salt
4tsp caster sugar
100ml rice vinegar
6 slices avocado
To make the mayonnaise whisk the egg wasabi and vinegar. Whisk in the oil a few drops at a time to form an emulsion. Incorporate the syrup and reserve.
Meanwhile sprinkle salt and sugar over the fish fillet on both sides. Lay skin-side down in a dish and refrigerate for two hours. Combine vinegar sake and mirin. Coat the fillet with this and marinate for an hour more.
To serve slice the fillet into 18 pieces on the slant. For each portion put a halved avocado slice on the plate coat with a tablespoon of mayonnaise and arrange three snook slices on top.