1. Preheat a barbecue to medium-high with hood closed. Rinse fish under cold running water. Pat dry with paper towel. Make 3 shallow cuts, 1cm-deep, in thickest part of each side of fish.
2. Place a large sheet of baking paper on top of a large sheet of foil on a flat surface. Place fish in centre of paper. Fill with lemongrass, garlic and lime leaves. Season fish with salt and pepper. Fold up baking paper and foil to enclose fish.
3. Barbecue the fish, with the hood closed, for 30 to 35 minutes, turning halfway, or until cooked through.
4. Meanwhile, make dressing: Combine sweet chilli sauce, lime juice, sugar, soy sauce, ginger, fish sauce, oil and coriander in a jug.
5. Unwrap fish and serve. Drizzle with dressing. Top with coriander sprigs and green onion. Serve with lime wedges and rice.