Cut out 4 x 30 cm (12 inch) squares of nonstick baking paper and brush the centres of each with a little sesame oil. Place a piece of fish in the centre of each square. Mix together the mushrooms, sugar snap peas and chilli and pile on top of the fish.
Mix together the remaining oil, ginger and garlic and spoon over the vegetables. Bring the sides of the paper up over the fish as though wrapping a parcel. Fold the edges together and flatten gently.
Flatten the ends and fold them over to seal. Place the parcels on a baking sheet and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 20 minutes. Open 1 of the parcels and test whether the fish is cooked through. If necessary, return to the oven for a few more minutes.
Meanwhile, mix together the soy sauce, lime juice, sweet chilli sauce and coriander. Loosen the parcels and spoon the dressing over the fish before serving.