Put the chicken or vegetable stock in a large pan with the ginger, soy sauce, oil and five-spice powder. Bring to boil and allow to simmer gently for 10 minutes.
Blend the cornstarch in a measuring cup with 4-5 tablespoons water and stir into stock. Cook, stirring constantly, until slightly thickened. Season with salt and pepper to taste.
In a pitcher, beat the eggs together with 2 tablespoons cold water until the mixture becomes frothy.
Bring the soup back to boil and drizzle in the egg mixture, stirring vigorously with chopsticks. Choose a pitcher with a fine spout to form a very thin drizzle. Serve at once, sprinkled with sliced scallions and chopped cilantro.