Break rice noodles, if using, into a large bowl; cover with warm water. Let stand for 15 minutes while preparing chicken mixture.
Drain pineapple, reserving juice (you should have about 1/3 cup). For sauce, in a small bowl stir together the reserved pineapple juice, the chicken broth, vinegar, brown sugar, cornstarch, and soy sauce. Set aside.
Heat the oil in a wok or large skillet over medium-high heat. (Add more oil as necessary during cooking.) Stir-fry garlic in hot oil for 15 seconds. Add celery and onion; stir-fry for 2 minutes. Add the sweet pepper; stir-fry for 2 minutes more. Remove vegetables from wok.
Add the chicken to the hot wok. Stir-fry for 2 to 3 minutes or until no longer pink. Stir sauce; add to wok. Cook and stir until thickened and bubbly. Add cooked vegetables and pineapple. Cook and stir for 2 minutes more or until heated through. Drain rice noodles, if using; arrange noodles or hot cooked rice on 4 dinner plates. Top with chicken mixture. Makes 4 servings.