Cut pork slices into strips about 3 inches long and 1/2 to 1-inch wide. Heat the oil in a medium skillet and saute pork strips over medium heat until lightly browned. Drain the pineapple and reserve the juice. Combine pineapple juice, 3/4 cup water, vinegar, soy sauce, brown sugar, and salt; pour over pork in the skillet. Cover and simmer over low heat for 1 hour, or until meat is tender. In a cup, combine cornstarch and 2 tablespoons water; stir until smooth. Add cornstarch mixture to pork and cook over low heat, stirring constantly, until mixture is thick and bubbly. Add pineapple chunks, onion and green pepper. Cover and simmer sweet and sour pork for 10 minutes longer, or until vegetables are tender. Serve sweet and sour pork over rice.