Season pork pieces on all sides using entire packet of seasoning.
Set InstaPot to sauté mode, and add oil. Working in batches as needed, add seasoned pork pieces and cook undisturbed for two minutes on at least 2 sides. When all pieces are browned, add sliced onion, water, and lime juice. Stir to combine.
Seal InstaPot and set to cook at high pressure for 30 minutes. Allow for natural release for 5 minutes, and then carefully use the quick release method for any remaining pressure.
Use tongs to remove pork pieces to a large bowl and use two forks to shred pork. Reserve cooking juices for broiling step.
When ready to serve, heat broiler to high. Working in batches to avoid overcrowding, spread shredded pork and pineapple chunks onto a baking sheet and spoon 1 cup reserved cooking juices over. Broil for 5-10 minutes or until most liquid has evaporated and pork and pineapple are browned and crispy. Serve immediately with your favorite taco toppings.