In a medium saucepan, bring the stock to a simmer.
Add 6 tablespoons of scallions, the spinach (or arugula), mushrooms, soy sauce and white pepper. Return to a low simmer and cook for 3 minutes.
Stirring with a fork, gradually add the eggs in a slow steady stream. Cook until the eggs are set, stirring to create shreds or ribbons of the eggs, 1 minute.
Remove saucepan from the heat.
Ladle soup into bowls, garnish with remaining scallions.
Season with salt to taste and serve immediately.