Preheat the oven to 375 degrees Cut the onion into quarters. Slice the pork roast into chunks. Season the pork chunks with kosher salt and place into a 9x13 inch baking dish. Cut the orange slice into quarters and squeeze the juice over the pork chunks. Nestle the squeezed orange chunks into the casserole. Nestle in onion quarters, garlic cloves, bay leaves, and cinnamon sticks. Pour vegetable oil evenly on top of the pork.
Cover the dish tightly with aluminum foil. Place into the oven and cook until the pork is tender, about 3 ½ hours.
Remove from the oven and remove the oranges, bay leaves, and cinnamon. Shred the pork if desired using two forks. Place under the broiler until the meat is crisp and brown on the surface. Serve on corn tortillas with your favorite condiments.