Heat a large saucepan over a medium heat and add the oil. Once hot, add the chicken strips and cook until golden brown, about 4–5 minutes. Remove from the pan, cover and keep warm.
Add the mushrooms, garlic and ginger to the hot pan and cook, stirring, for 2–3 minutes. Pour in the stock and cook for 10–15 minutes.
In a bowl, whisk the egg, sesame oil, soy sauce, chilli oil and vinegar.
Tip the egg mixture into the broth while it’s still warm, mixing constantly. It doesn’t look great at this stage but stick with it. Add the cooked chicken and let it warm through.
To serve, ladle the broth into warmed serving bowls and garnish with the spring onions (scallions), red chilli and a drop or two of sesame oil.