Cut 4 x 30 cm (12 inch) squares of nonstick baking paper and brush the centres with sesame oil. Place a fish fillet in the centre of each square. Mix together the mushrooms, sugar snap peas and chilli, then divide between the paper, piling on top of the fish. Bring the sides of each square up around the fish to form 'cups'.
Mix together the sesame oil, ginger and garlic and spoon over the vegetables. Fold the edges of the paper to seal and form parcels and place on a baking tray.
Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 20 minutes, or until the fish is cooked through (open a parcel and check the flesh is opaque in the centre).
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.