Cut broccoli into florets, cook florets in boiling salted water for about 3 minutes until al dente. Drain and rinse under cold water. Cut the florets into smaller pieces. Clean, wash and slice the mushrooms.
Wash the chicken, dab dry and cut into thin slices. Peel ginger and chop very finely. Clean and wash the chilli and cut into thin rings. Wash and clean spring onions and cut them into thin rings.
Bring the stock, coconut milk, ginger and chilli to the boil and simmer for about 20 minutes. Season to taste with salt, soy sauce and lemon juice. Add the chicken, mushrooms, broccoli and spring onions and simmer for about 3 minutes.
Wash the coriander, shake dry and chop the upper 1/3 of the stalk finely. Season soup again. Add coriander. Serve soup in bowls. Sprinkle with some chilli oil if necessary.