In a pot over medium heat, add a small drizzle of oil. Sauté the garlic and the green onion until fragrant, about 30 seconds.
Add the chopped tomatoes and cook for 4–6 minutes, stirring occasionally, until they break down and look soft and saucy.
Add the soy sauce and mix, then pour in the water (or stock) and bring to a boil.
Stir your cornstarch slurry, then slowly pour it into the soup while stirring until the broth looks slightly glossy and lightly thickened.
Turn the heat to low, then slowly stream in the beaten eggs with a chopstick. Allow to set and float before gently stirring in one direction to form soft ribbons.
Add salt, white pepper, and sesame oil, then stir in the cilantro if using. Taste and adjust seasoning as needed.
