1In a bowl, combine fish sauce, juice, chilli and sugar. Set aside until ready to use.
2Score fish in the thickest part at 3-cm intervals on both sides. Stuff each cavity with quarter ginger, lime slices and 1 coriander sprig. Season skin with salt.
3Place a large steamer basket over a wok of rapidly simmering water. Arrange fish on a heatproof plate or baking paper in steamer. Cover and steam 10 to 12 mins, until flesh flakes easily.
4Top with combined cucumber, coriander leaves, green onions and chilli. Spoon sauce over and serve with lime wedges.
The flavour is improved by a good quality fish sauce. Look for "ca com" on the label, indicating only anchovies were used in the making. The colour should look like tea, light and very clear.
Photo: Bauer/Rob Shaw