Bring the water and soy sauce to a boil in a saucepan. In the meantime, mix the starch with a little water and whisk the egg. As soon as the water boils, add the stock cubes. After a short further boiling, stir in the tomato paste.
Now add the Asian vegetables and bring to the boil again. Add starch, vinegar, sugar and salt. Finally, pour the egg slowly into the soup, stir gently, remove the saucepan from the hob and stir in the sambal oelek.