Place all ingredients, except for the bay leaves, into the slow cooker bowl.
Gently toss everything together with tongs, then add the bay leaves.Cover and cook on low for 8 to 9 hours or on high for 4 to 5 hours, until the beef is tender and shreds easily with a fork. If it's not shredding easily, continue cooking for a bit longer.
Transfer the beef to a cutting board and shred it using two forks.
Return the shredded beef to the slow cooker, stir it to combine, and allow it to soak up the juices.
Serve the barbacoa directly from the slow cooker, or transfer it to a serving dish and garnish with chopped cilantro and lime wedges.
Using tongs, take a portion of barbacoa from the slow cooker and place it on a tortilla. Garnish with diced onions, avocado, cilantro, and any other desired toppings.