Preheat the oven to 180°C.
Layer four sheets of filo pastry, brushing each layer with melted clarified butter.
Cut 10cm circles from the pastry and press them into tartlet moulds.
Cover the pastry with parchment, fill with baking beans, and bake for 15 minutes.
Blend oysters, egg yolk, mustard, salt, pepper, lime juice, and oil into a mayonnaise consistency.
Combine diced mackerel, shallots, capers, ginger, soy sauce, lime juice, chives, and oyster mayonnaise.
Boil vinegar, sugar, chilli, and ginger, then cool and pour over cucumber strips.
Fill the pastry cases with the mackerel mixture and top with pickled cucumber.