In a bowl, mix together chicken, sliced shiitake mushrooms, 1 tablespoon of oyster sauce, soy sauce, vinegar, salt, white pepper powder, sesame oil & cornflour. Marinate for 10 minutes.
2 boneless chicken thighs, 1 tablespoon + 1 teaspoon oyster sauce, 1 tablespoon light soy sauce, 1 teaspoon vinegar, ¼ teaspoon salt, ½ teaspoon white pepper powder, 1 teaspoon toasted sesame oil, ½ tablespoon cornflour