In stock pot over medium heat, bring chicken broth to a simmer. Slowly stir in egg whites. Season to taste with salt and pepper. Heat through until whites are thoroughly cooked.
To serve, portion about 1/2 ounce shiitakes, 2 teaspoons green onions and 1 teaspoon cilantro into a soup bowl. Pour 1-1/2 cups eggs and broth into each bowl. Serve immediately.
Note: Do not let uncooked egg mixture remain at room temperature for longer than one hour (including preparation and service time).