In a pan, combine the chicken stock, water, mushrooms, bamboo shoots, root ginger, garlic, soy sauce and crushed chillies. Bring to the boil, then reduce the heat to low, cover and simmer while you assemble the rest of the ingredients.
Place the chicken strips into a bowl and toss with the sesame oil to coat. In a separate bowl, stir together the cornflour and vinegar, and set aside.
Increase the heat under the stock to medium-high, and return to a rolling boil. Add the chicken. Return to the boil, and then drizzle in the egg while stirring slowly to create long strands of egg. Stir in the vinegar and cornflour. Simmer over medium heat, stirring occasionally, until chicken is cooked through and the stock has thickened slightly, about 3 minutes. Serve garnished with spring onions and coriander.