Begin by making the rub. In a bowl, combine the salt, pepper, garlic powder, oregano, cumin, and oil. Mix to form a paste.
Rub the seasoning all over the outside of the meat. Wash your hands thoroughly.
Place the shoulder into your slow cooker.
Top with the chopped onion, jalapeño, garlic cloves, orange zest, and juice.
Turn your slow cooker to low and cook, covered, for 5-6 hours until the meat is falling apart.
Remove the shredded meat from the slow cooker and place onto a baking sheet.
Preheat the oven to 450 degrees F.
Toast the meat until the top has browned and crispy edges, about 10-15 minutes.
Remove from the oven and serve on tortillas with toppings of your choice. Drizzle more cooking juices over the top.