Combine the first 5 ingredients in a bowl and set aside.
Place the pork and cornstarch in a second bowl and toss to combine. Heat the 1/3 cup vegetable oil in large, wide skillet or large wok set over medium-high heat. When hot, add the pork, in batches, quickly brown on all sides, and then transfer to a plate
Clean the cooking pan, set back over medium-high heat and add the 1 Tbsp. oil. When very hot, add the pineapple, bell pepper, onion, garlic and ginger and stir-fry 2 to 3 minutes. Return the pork to the pan and add the ketchup mixture. Bring to a simmer, and simmer 1 to 2 minutes. Spoon the pork onto a serving platter or shallow bowl, sprinkle with green onion and enjoy.