Preheat the oven to gas 6, 200°C, fan 180°C. Arrange four large pieces of nonstick baking paper on a tray. Put one fish fillet in the middle of each and top with the chilli, and ginger, then season. Fold up the sides and roll the edges together to make a loose parcel, leaving room for the steam to circulate while it cooks. Bake for 8-10 minutes, until cooked through.
To make the dressing, combine all the ingredients in a small bowl and mix well. Spoon a little of the dressing over the fish to serve.