Before starting, get all the toppings you want ready; figure about 1 cup total per serving. (See the recipe note for some ideas.)
Put the stock and soy sauce in a large pot over medium-high heat and bring to a boil. Meanwhile, crack the eggs into a medium bowl; something with a pour spout is ideal but not necessary. Add a sprinkle of salt and pepper and beat with a fork or whisk until no streaks remain.
When the stock is boiling, adjust the heat so that it bubbles gently and steadily, but not furiously. Pour the eggs into the stock in a slow stream, stirring constantly in slow swirls with a large spoon. You want them to scramble softly without clumping or dissolving into the soup, so it’s important to keep the liquid moving slowly until the eggs are cooked, 1 to 2 minutes.
Stir in the scallions and sesame oil, then taste and adjust the seasoning with more salt, pepper, soy sauce, or sesame oil. Serve, garnished with the cilantro and prepared extra toppings from Step 1.