Rub taco seasoning or spice mixture over meat. Place brisket in the slow cooker with onions and garlic. Add broth and beer. Set to the Low heat setting and cook for 6-8 hours until meat is falling apart.
Remove brisket from the cooker and shred with two forks on a plate or cutting board. Place meat back in the cooker with juices to keep warm.
Serve in corn or flour tortillas with lime wedges and your favorite taco fixings, such as diced onions, tomatoes, sour cream, salsa, cilantro, guacamole, and shredded Jack cheese.