Cut the fish into approx. 2 cm cubes. Press the garlic, combine with the sherry, oil and fish sauce, add to the fish and mix well, cover and leave to marinate in the fridge for approx. 30 mins.
Chop the onion and sauté in the butter. Add the rice, sauté until translucent. Pour in the stock, bring to the boil, reduce the heat, cover and simmer over a medium heat for approx. 15 mins.
Cut the Chinese leaves into strips and the mushrooms into pieces, add to the rice, continue to simmer for approx. 5 mins.
Wipe the marinade off the fish. Pat the fish dry. Heat the oil in a frying pan, fry the fish for approx. 3 mins., season with salt. Finely chop the dill, add to the rice along with the fish, mix carefully, heat gently, season.