Simmer the fish trimmings, onion, and 500ml of boiling water for 15 minutes.
Sieve the broth into a clean saucepan and discard the solids.
Place greased silicone paper in a bamboo steamer over boiling water.
Set the fish skin-side down on the paper and season with salt and pepper.
Scatter soy sauce, sesame oil, ginger, chives, and coriander over the fish.
Cover and steam the fish for 7 minutes until opaque and cooked through.
Heat the broth with the cooked noodles and pour into a serving bowl.
Place the steamed fish into the noodle broth and serve.