Preheat a barbecue plate on medium heat. Lightly spray four 30cm x 40cm sheets of baking paper with oil. Place 1 piece of fish on each piece of paper. Top with the mushrooms, chopped coriander and green onions.
Combine the sugar, fish sauce, ¼ cup lime juice and sweet chilli sauce in a small jug. Spoon sauce mixture over the fish.
Bring the long sides of the paper together and fold over to secure. Fold the short sides up to form a parcel. Place parcels, seam-side up, on the barbecue plate. Cover with a hood or a large roasting pan. Barbecue for 10–12 minutes or until fish is cooked to your liking.
Open parcels. Top with coriander sprigs. Serve with rice and lime wedges.