In a small bowl, combine cornstarch and water until smooth; set aside. In a large skillet or wok, cook pork in oil until browned. Add the pineapple, corn syrup, vinegar, ketchup, soy sauce and garlic. Bring to a boil. Reduce heat; simmer, uncovered, for 10 minutes.
Add the green pepper; cook for 2 minutes. Stir the cornstarch mixture and stir into pork mixture. Bring to a boil; cook and stir for 2 minutes or until thickened and green pepper is crisp-tender. Serve over rice if desired.