Drain pineapple, reserving juice; set pineapple chunks aside. Combine juice, vinegar, soy sauce, sherry, sugar, 2 Tbsp cornstarch and salt, stirring until cornstarch dissolves; set aside.
Combine water, flour, 1/2 cup corn starch, baking soda, and 1 tsp. sugar in a small mixing bowl; stir until smooth. Add chicken pieces to batter, stirring until well coated. Heat oil in a wok to 375 degrees; cook half the chicken in oil until lightly browned. Drain on paper towels; Set aside. Repeat with remaining chicken, set aside.
Drain oil from wok, reserving 2 Tbsp. in wok. Heat wok to 350 degrees. Add green pepper, onions and pineapple chunks. Stir-fry 1 to 2 minutes or until crisp-tender. Remove from wok; set aside.
Stir cornstarch mixture and add to wok. Cook stirring constantly until smooth and thickened. Add reserved chicken, vegetables and pineapple; stir gently and cook until thoroughly heated. Serve over rice. Yield 4 servings