Trim fat from pork. Cut pork into 1 inch cubes. Cut onion into 8 wedges. Cut pepper into 1 inch pieces. Cut peaches in half; discard pits. Cut each peach half into 6 wedges. Set aside.Drain pineapple, reserving the juice in a cup. Add vinegar, sugar, cornstarch, and soy sauce to the pineapple juice; stir until smooth. Set asideHeat the wok over medium high heat until hot. Drizzle oil into the wok and heat 30 seconds. Add pork and stir fry about 7 minutes or until well browned. Add onion and stir fry 2 minutes or until onion is tender. Stir in pepper and stir fry 1 minute. Reduce heat to medium.Stir cornstarch mixture until smooth; add to the wok. Add peaches and pineapple; cook and stir until sauce boils and thickens. Transfer to serving dish. Serve with rice.