Heat oil in a saucepan over medium low heat. Add the tomatoes and stir fryfor 5 min until they are softened and start to fall apart.
Add in chicken stock, water, soy sauce, sesame oil, pepper and salt to taste.
Bring to a boil, and then lower the heat so that the soup is simmering with the lid on.
Now quickly beat the egg in a small bowl and prepare the cornstarch slurry in a separate bowl.
Use a ladle to slowly swirl the soupin a whirlpool motion. Keep swirling as you pour in the cornstarch slurry until well incorporated.
Now pour a thin stream of egg into the middle of the whirlpool as you slowly swirl the soup. This is how you get that pretty egg ribbons.
Turn off heat as soon as egg ribbons are formed.
Serve hot or at room temperature. Ladle soup intobowls and garnish with chopped scallions and cilantro.