1. For the pickled green chillies, place the vinegar and sugar into a small stainless-steel saucepan and bring to the boil, stirring to dissolve the sugar. When the sugar has dissolved, remove from the heat and leave to cool. Meanwhile, pack the green chilli slices into a sterilised glass jar. When the pickling liquid has cooled, pour it over the chillies, then seal the jar and refrigerate. Leave for a month before using.

2. For the salted red chillies, rinse and dry the chillies. Trim off the stems and roughly chop, then mix with ¾ of the sea salt in a bowl. Pack the red chilli and salt mixture into a sterilised glass jar, sprinkle with the rest of the sea salt and seal. Store in a cool, dark place for at least 2 weeks before using. Refrigerate after opening.

3. Place the trevalla on a lightly oiled heatproof plate that will fit in your steamer, then spread a layer of pickled green chillies over one half of each fillet and a layer of salted chillies over the other half and place in the steamer. Drizzle the fish with the soy sauce and pickled chilli juice and steam over boiling water for about 6 minutes, until each fillet is just cooked.

4. Carefully lift the fish from the steamer and place on a serving dish. Stir the sesame oil into the cooking juices on the plate in the steamer, then pour the mixture around the fish, taking care not to disturb the green and red chilli coating. Serve immediately. 

Note: This spinach, chilli and sesame salad is the perfect accompaniment to this dish.