Make the marinade by mixing together the sugar, salt, soy sauce and cornflour slurry. Mix in the chicken, turn to coat, allow to marinate for 20 minutes.
Marinate the shiitake mushrooms in soy sauce, sugar and sesame oil for 20 minutes.
Heat a large frying pan with 1 tablespoon oil over high heat. Stir fry the garlic and ginger until fragrant, 2-3 minutes. Add the onion and salt, stir fry until soft, about 3-4 minutes.
Stir in the shiitake mushrooms and stir fry for 1-2 minutes. Add the chicken and stir fry until brown, 3-4 minutes. Add the sliced cabbage and bamboo shoots, stir well.
Mix in the water and heat through, 1-2 minutes. Reduce the heat to low and simmer until the cabbage is soft, around 7 minutes. Add the oyster sauce, sugar and sesame oil, stir well and serve.