In a medium bowl, mix pork tenderloin, mirin, and 1/4 teaspoon salt. Add 1 tablespoon cornstarch and mix again, until pork is evenly covered. Marinate for 10-15 minutes. In a small bowl mix together rice vinegar and white pepper and set aside.
In a pot on medium high, add water. Add tomato, mushroom and tofu, cover, and bring to a boil. Turn heat down to medium low, add shoyu, and boil without lid for 5 minutes.
Mix remaining cornstarch with 2 tablespoons of water in a bowl until cornstarch is fully dissolved. Slowly add cornstarch-water mixture into soup, stir well. The soup should be thickened but not too heavy. Add pork into soup; stir several times to avoid the pork strips sticking together. Add remaining 1 teaspoon salt. Slowly swirl in the beaten egg and stir well. The egg should be scattered and not clotted.
Add vinegar and pepper mixture; stir well, then remove from heat immediately. Add Chinese parsley and sesame oil, give a final stir. Serve while warm. Serves 5.
Approximate Nutrient Analysis per serving:
130 calories, 4.5 g fat, 1 g saturated fat, 50 mg cholesterol, 750 mg sodium, 15 g carbohydrate, 1 g fiber, 3 g sugar, 9 g protein