Combine egg and salt, beating with a wire whisk until frothy. Set aside. Combine soy sauce, oil, and sugar. Set aside.
Coat a wok with cooking spray. Heat at medium-high (375°) until hot. Add celery and onion; stir-fry 2 minutes. Add mushrooms, tofu, and garlic; stir-fry 1 minute.
Push vegetable mixture up sides of wok, forming a well in center. Pour egg mixture into well, and stir-fry until set. Add rice, and stir-fry 1 minute. Add soy sauce mixture and peas; stir-fry 2 minutes. Serve immediately.