Heat oil in a large saucepan over medium heat. Add the red bell pepper and green onions and saute for 5 minutes. Then, add the 2 cups water, broth and soy sauce, reduce heat to medium low and simmer for 5 minutes.
In a separate medium bowl, combine the vinegar, red pepper flakes, ground black pepper, cornstarch, 3 tablespoons water and sesame oil. Add this to the soup and continue to simmer for 5 more minutes, or until soup becomes thick and bubbly.
Finally, mix in the tofu, snow peas and water chestnuts, and continue cooking 10 minutes, or until heated through.
