Trim fat from beef. Partially freeze beef. Thinly slice across grain into bite-size strips. Set aside.

Peel and section orange. Cut sections in half lengthwise. Set aside.

For sauce, drain pineapple reserving juice. Pour 1/2 cup of the reserved juice into a small bowl. (Reserve remaining juice for another use.) Stir in vinegar, soy sauce, cornstarch, brown sugar, and ground red pepper. 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 pepper and onion in hot oil for 3 to 4 minutes or until crisp-tender. Remove vegetables 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 cooked vegetables to the wok. Add pineapple chunks. Stir all ingredients together to coat with sauce. Cook and stir for 2 minutes more or until heated through. Stir in orange slices. Serve immediately over hot cooked rice. Garnish with additional orange sections, if desired. Makes 4 servings.

Prepare vegetables; cover and chill up to 4 hours.