Turn slow cooker on high. Add onion, lime zest and juice, orange zest and its juice, garlic, cumin, oregano, Jalapenos (if using), bay leaves, 3 teaspoons salt and 2 teaspoons pepper. Stir to combine. Rinse and dry the pork shoulder or butt with paper towel. Sprinkle roast with salt and pepper. Rub seasoning into roast. Place roast in slow cooker, fat side up. Cover and cook until pork roast is tender; between 3-4 hours on high or 6-8 hours on low. Cooking time will depend on size of pork roast. The pork should fall apart easily when poked with a fork.
Once the pork is cooked transfer to a large bowl. Using two forks, shred the pork. Do not discard the juices in the slow cooker. If you like, skim excess fat off the top of the juices and discard. You also have the option of straining the liquid through a strainer to remove the onions and little bits. I don't usually do any of this. It's your choice. Remove the bay leaves,
Put oil in a large skillet, over medium to medium-high heat. Heat until it shimmers or a drop of water flicked in it dances. Add the pork. Whisk cooking liquids in slow cooker. Scoop out 1 cup and add it to the skillet. Cook, stirring occasionally, until the liquid has almost evaporated and pork is brown and crispy in spots; about 10 to 15 minutes. Press the pork on to the bottom of the skillet and leave it to brown for a minute or two. Turn over and repeat. Season with salt and pepper to taste. Transfer pork to an oven-safe serving bowl and place in oven to keep warm. Add about ½ cup of the remaining cooking liquid in your slow cooker to the pork to keep it moist while in the serving dish.
Warm tortillas, according to package instructions, if desired. Place all of the toppings in small bowls or on a large cutting board so everyone can make up their own. Smear some refried beans in the center third of the tortilla. Add the cheese, pork and sour cream. Then add the vegetables, cilantro and salsa. Finish it off with a squeeze from a wedge of lime. Fold up the bottom edge and roll from the side. Leave one end open.
Now to deal with leftovers. Pork freezes beautifully. 1. FREEZER If you have enough leftover, place pork into a container and add between ½ and 1 cup of cooking liquid. Add a little more if you like. Too much juice is better then not enough! Make your portion size according to your needs and convenience. Remember to add cooking juices to each portion prior to placing it into a freezer bag or container. When ready to use the leftovers, totally defrost. Heat oil in skillet and add meat mixture. While the meat is browning and crisping, prepare your favorite taco ingredients. 2. REHEAT If reheating the pork from the night before, put some oil in a skillet and heat the pork. If you prefer, use your microwave to reheat. 3. MAKE AHEAD You can prepare the pork up to three days ahead. Store pork in the refrigerator, separate from the cooking juices. When ready, shred pork and heat up some oil in a skillet. Toss until pork is brown and crisped up for serving.
Instead of rolling up tortillas, serve pork mixture in tortilla bowls instead. It's almost like eating a delicious salad! You might want to check them out.