Peel and slice the ginger as finely as possible. Cut across into thin shreds and mix with the crushed chillies, garlic and 1 teaspoon of the vinegar. Spoon over the pieces of cod, rubbing it in gently.
Lightly oil a wire rack and position over a small roasting pan. Pour the stock into the pan and place the cod fillets on the rack. Cover with foil and carefully transfer to a preheated oven, 180°C (350°F), Gas Mark 4, for 20 minutes or until cooked through.
Meanwhile, peel the cucumber, cut in half and scoop out the seeds. Cut the flesh into small, chip-sized pieces. Mix together the soy sauce, oyster sauce, sugar and remaining vinegar in a small bowl.
Remove the fish from the pan and keep warm. Drain off the juices from the pan and reserve. Add the cucumber, spring onions, coriander and rice to the pan and heat through, stirring, for about 5 minutes until hot, stirring in enough of the reserved juices to make the rice slightly moist.
Pile on to serving plates, top with the fish and serve with the sauce spooned over.