Partially freeze pork; trim fat from pork. Slice pork diagonally across grain into thin slices; slice into 1-inch-wide strips. Coat a nonstick skillet with cooking spray; place over medium-high heat until hot. Add pork; cook 8 minutes or until browned, stirring frequently. Remove from skillet. Drain and pat dry. Wipe drippings from skillet with a paper towel.
Combine pork, tomato sauce, and next 5 ingredients in skillet; bring to a boil. Cover, reduce heat, and simmer 15 minutes or until pork is tender. Drain pineapple, reserving juice. Add enough water to juice to make 1 cup liquid. Set aside. Add pineapple, green pepper pieces, and green onions to skillet; cover and simmer 5 to 7 minutes or until vegetables are crisp-tender. Combine cornstarch and reserved pineapple juice mixture; stir into pork mixture. Cook, stirring constantly, until thickened. Spoon pork mixture over rice. Garnish with pepper triangles, if desired.