Marinate beef in 2 tablespoon soy sauce and 1/4 teaspoon pepper for 30 minutes. Drain and reserve marinade.
Stir fry beef in batches in 2 tablespoon oil until cooked. Set aside.
Using the same pan, add 1 tablespoon oil (if needed) and saute garlic, onion and carrot.
Add mushrooms and cook for 3 minutes. Set aside.
Again, using the same pan, combine marinade, mushroom stock, tomato sauce. 3/4 cup water, soy sauce and sugar.
Cover and simmer for 10 minutes over low heat.
Add meat and vegetable mixture. Simmer for another 5 minutes. Add celery.
Simmer again for a few seconds. Serve hot.