Wash the chicken breast and put it in a large pot. Peel and chop the onions. Clean 150 g mushrooms. Peel carrots and cut them into pieces. Remove the outer rind from the lemon grass, chop the inside roughly.
Peel 10 g ginger and garlic and crush them coarsely in a mortar. Clean 1 chilli, cut lengthwise, wash and remove seeds. Cut the pod into small pieces. Add onions, carrots, mushrooms, lemon grass, ginger, garlic and chilli to the chicken breast.
Add 1 1/2 litres of cold water so that the meat is covered. Salt a little, bring everything to the boil and simmer at low heat for 1-1 1/2 hours. Remove any foam with a skimmer.
Clean the remaining mushrooms and cut them in half. Peel 10 g ginger and cut into fine strips. Clean 1 chilli, cut lengthwise, wash and remove seeds. Cut the pod into small pieces. Clean, wash, halve and slice the zucchini.
Wash and clean the tomatoes, grate them dry and cut them in half.
Lift the chicken breast out of the stock and let it cool down a little. Remove the skin and remove the meat from the bones. Pluck the meat. Pour the broth through a fine sieve into a pot, bring to the boil and boil down over a high heat for about 5 minutes.
Add mushrooms, ginger, chilli, zucchini and chicken pieces and simmer for 5-6 minutes at medium heat. Add tomatoes and coconut milk about 2 minutes before the end of cooking time. Season to taste with soy sauce, sugar and lime juice.
Wash coriander, shake dry and pluck leaves. Divide soup into bowls and sprinkle with coriander.