Heat oil in a pot over medium heat. Add the tomato chunks and stir-fry until they soften, about 5 minutes.
Pour in the chicken stock. Add soy sauce, toasted sesame oil, ground white pepper, and salt to taste. Bring the mixture to a simmer.
Slowly stir in the cornstarch slurry until the soup slightly thickens. Create a gentle whirlpool with a spoon and slowly drizzle in the beaten egg to form fine ribbons.