Place snapper on a heatproof plate that fits snugly into a large steamer, scatter over ginger and onion, drizzle with Shaoxing and soy sauce, cover and steam over a wok of boiling water until fish is cooked through (8-10 minutes).
Meanwhile, heat 15ml peanut oil in a large frying pan or wok over high heat, add water spinach and garlic and stir-fry until wilted and bright green (2-3 minutes).
Heat sesame oil and remaining peanut oil in a small saucepan until smoking (1-2 minutes). Transfer fish to plates, drizzle over juices, then pour over hot oil, scatter with extra spring onion, chilli and coriander and serve with rice and water spinach.
