Make sure the fish is well scaled and wipe down with a paper towel. Cut fish through to the bone from head to tail at 3cm intervals on both sides.
Put oil in a large wok or a saucepan big enough to fry the whole fish. Heat oil to 180°C or until a cube of bread turns golden in 30 seconds.
Dust fish in a mixture of flour and salt, then shake off any excess. Carefully slide the whole fish into the wok and fry for about 5 minutes, then turn the fish over and repeat on the other side. The fish should be golden on the outside and the flesh just cooked through to the bone.
Remove the fish from the pan and drain on a paper towel. Remove excess oil from the wok and wipe clean.
Heat wok again with 2 tbsp vegetable oil until just smoking and stir-fry ginger, spring onions (whites only) and capsicum until fragrant. Deglaze wok with Shaoxing wine, then add stock, soy sauce, sugar, vinegar and tomato sauce. Bring to a boil and simmer until thickened slightly. Add the pineapple and the green ends of the spring onions and cook for 30 seconds.
Transfer the fish to a serving dish and spoon the sauce over the top. Sprinkle with sesame oil and coriander leaves, then serve immediately.