Freeze the fresh chicken breast a little, let frozen food thaw. Cut approx. 2 mm thick slices across the grain and cut in half lengthways and crossways. Mix the ingredients for the marinade and use them to marinate the chicken for 20 minutes. Bring the coconut water to the boil, dissolve the mushroom bouillon in it and soak the shiitake mushrooms for 30 minutes.
Wash the vegetables. Cut the white part of the lemongrass crosswise into approx. 6 cm long pieces and gently loosen the lower two thirds by tapping with the back of a knife. Peel the galangal and cut it crosswise into thin slices. Remove the stems from the tomatoes, cut in half lengthways, remove the green stalk and the grains. Halve the halves lengthways. Remove the stems from the peppers, wash them, cut in half lengthways, core and cut across into thin strips.
Squeeze out the mushrooms and cut the hats into bite-sized pieces. Put all of the mushroom broth in a saucepan. Add rice wine vinegar, lemongrass, galangal, kaffir lime leaves and chillies and simmer for 15 minutes. Strain, keep the stock, leaves and lemongrass, discard the rest.
Mix the coconut milk into the broth and let it simmer. Add tomatoes, peppers and mushrooms and let simmer for 2 minutes. Mix in the chicken pieces together with their marinade and squeeze the garlic. Let simmer for another 3 minutes.
Distribute the finished soup on the serving bowls, garnish as desired, serve and enjoy warm.