Trim fat from beef. Partially freeze beef. Thinly slice across grain into bite-size strips. Set aside.
For sauce, in a small bowl stir together orange peel, orange juice, cornstarch, soy sauce, sugar, and bouillon granules. Set aside.
Pour cooking oil into a wok or large skillet. (Add more oil as necessary during cooking.) Preheat over medium-high heat. Stir-fry green onions and garlic in hot oil for 1 minute. Remove green onion mixture from the wok.
Add beef to the hot wok. Stir-fry for 2 to 3 minutes or until cooked through. Push beef from the center of the wok.
Stir sauce. Add sauce to the center of the wok. Cook and stir until thickened and bubbly. Return green onion mixture to the wok. Add spinach and water chestnuts. Stir all ingredients together to coat with sauce. Cover and cook for 1 minute more or until heated through. Serve immediately over hot cooked rice. Sprinkle with slivered orange peel, if desired. Makes 4 servings.