Cut the tenderloin into thin slices and place in a bowl. Add the five-spice powder, salt, pepper, chili powder, soy sauce, and 1 tablespoon cornstarch. Set aside.
In a medium bowl, mix all the ingredients for the sauce and place it near the stove.
In a shallow dish, mix the remaining corn flour and flour. Add the pork, one piece at a time, to coat with the cornstarch-flour mixture. Once coated, remove any excess coating by gently shaking the bowl with the pork.
Heat the oil in a large frying pan and fry the pork in 3-4 batches until crispy. Remove with a slotted spoon and place in a bowl.
Drain the oil from the pan and wipe with paper towels (be careful, it is hot). Add 2 tablespoons of vegetable oil to the pan and sauté the ginger, garlic, and onion until fragrant and softened. Add the peppers. Sauté for about a minute to soften slightly, but not too much.
Return the pork to the pan and pour over the sauce. Leave to simmer and stir. Once the sauce has thickened and coats the pork, remove from the heat. Add the pineapple pieces and sprinkle with fresh onion. Serve with rice.