Dry the pork chunks well with a paper towel.
In a large bowl, add pork chunks, 1 tablespoon olive oil, oregano, salt, cumin, black pepper, orange juice, chipotle peppers, and beer. Combine mixture well with the pork until fully coated. Place the pork in a slow cooker, top with the onion, and minced garlic. Seal lid to the Instant Pot and cook on high pressure for 35 minutes.
Allow pressure to release naturally. Remove from pot and let cool slightly. Shred pork using two forks. Heat 1 tablespoon of oil in a large nonstick pan or cast-iron skillet over high heat. Add shredded pork in the pan (in batches) with some of the juices. Sear both sides of the until golden brown and crispy. Remove pork from skillet.
Wipe the pan clean with a paper towel. Add oil on medium-high heat until oil is hot and bubbly. Working in batches, fry the tortillas, turning once, until crispy, and golden brown, about 1 minute per side. Transfer the tostadas to a paper-towel-lined plate and sprinkle with salt immediately.
Top with carnitas and toppings of choice. Enjoy!