In a large bowl, stir together ground pasilla pepper, coriander, garlic, oregano, orange peel, black pepper, and salt. Add pork to bowl; toss to coat with spices.
In a 3- ½- to 4-quart slow cooker (see Tip), place pork mixture; top with onion wedges. Pour broth and orange juice over all.
Cover; cook on low-heat setting for 10 to 12 hours or on high-heat setting for 4- ½ to 5 hours.
Use a slotted spoon to remove meat from slow cooker. Using two forks, coarsely shred meat; discard any fat. Drizzle meat with some of the cooking liquid.
Wrap tortillas in foil. Heat in a 350°F oven for 10 minutes or until warm. To serve, top each tortilla with ¼ cup of the meat, some cilantro, and finely chopped green onions. Serve with salsa and, if desired, lime wedges.
Tip: For easy cleanup, line your slow cooker with a disposable slow cooker liner. Add ingredients as directed in recipe. Once your dish is finished cooking, spoon the food out of your slow cooker and simply dispose of the liner. Do not lift or transport the disposable liner with food inside.