To make the carnitas: Cut the pork shoulder into pieces of roughly 4 inches. Trim off and discard any large pieces of fat along the edges, and place the meat in the Instant Pot.
In a small bowl, combine lime juice, brown sugar, cumin, salt, oregano, chili powder, and garlic powder. Pour this mixture over the pork and rub in gently so that it coats each side of the meat.
Pour orange juice and water over the pork. Seal the lid and cook on high pressure for 40 minutes.
Allow a natural pressure release for 10 minutes, then turn the valve to “vent” to manually release remaining pressure. Open the lid, remove pieces of pork, and shred them by pulling apart with two forks into bite-size shreds. Leave liquid in the pot.
To crisp the carnitas by broiling: Spread the shredded pork out on a sheet pan. Turn oven to high broil setting. Place sheet pan approximately 4” below the heating element, close the door, and watch carefully — you’ll want to remove the pan when the top bits of pork turn brown and crispy, which should take just 2-3 minutes. If you desire lots of crispy bits, toss the meat a bit with tongs and place under the broiler for another 1-2 minutes. Meanwhile, set the Instant Pot to sauté to reduce the leftover cooking liquid. Transfer crisped pork to a large serving bowl, drizzle reduced liquid on top if desired, and serve.
Alternatively, to crisp the carnitas on the stovetop: Warm 1 Tablespoon avocado or olive oil in a large Dutch oven or non-stick skillet set over medium-high heat. When hot, add an even layer of the shredded pork to the skillet — don’t crowd it too much. Drizzle 2-3 Tablespoons of liquid from the Instant Pot over the pork and cook for 2-3 minutes, just until the liquid mostly evaporates and the pork has crispy, golden brown edges. Stir, cook 1 minute more, then remove pork from the skillet and place in a serving bowl. Add 2-3 Tablespoons more liquid from the Instant Pot to the pan, then scrape vigorously to remove any browned bits from the bottom. Let the liquid evaporate, then scoop out these crispy bits and add to the bowl with the pork. Add more oil to the skillet, and repeat as necessary until all the pork is crisped. (I can usually do this in two batches.)
Optionally, for extra sauce: After removing the last batch of pork and crispy browned bits, pour remaining liquid from the Instant Pot into the skillet. Add a pinch of salt and simmer over medium-high heat for 3-4 minutes, until noticeably thickened and reduced. Pour this rich sauce over the shredded pork, and toss very well to combine.
To make the salsa: Combine pineapple, jalapeño, cilantro, onion, salt, and lime juice in a small bowl. Be sure everything is chopped into relatively even, small pieces. Stir well to combine. Sample and add extra salt and/or lime juice to taste.
Assemble the tacos: Warm tortillas, dice avocado, and pull a few leaves of cilantro off of the stems. Pile tortillas with carnitas, salsa, avocado, a few cilantro leaves, and any other toppings as desired. Enjoy!