Drain pineapple, reserving juice; set pineapple aside. In a small bowl, combine the cornstarch, brown sugar, soy sauce, vinegar, ginger, garlic and reserved pineapple juice until blended; set aside.
In a large nonstick skillet or wok, stir-fry onion and red pepper in 2 tablespoons oil for 5 minutes or until crisp-tender. Remove and keep warm. In the same pan, stir-fry pork in remaining oil for 3-4 minutes or until no longer pink.
Stir soy sauce mixture and add to the pan. Bring to a boil; cook and stir for 2 minutes or until thickened. Stir in the carrots, onion mixture and reserved pineapple; heat through. Serve with rice if desired.