Pat the beef brisket dry with paper towels and trim away any large, thick pieces of surface fat, leaving a thin layer for flavor.

In a small bowl, mix together the kosher salt, black pepper, smoked paprika, garlic powder, onion powder, and ground cumin to create a dry rub.

Rub the spice mixture all over the brisket, coating every side evenly and pressing gently so the seasonings adhere.

Heat the olive oil in a large skillet over medium-high heat. When hot, sear the brisket for 3 to 4 minutes per side until nicely browned, then transfer it to the crock pot.

Add the sliced yellow onion and minced garlic to the same skillet and sauté for 2 to 3 minutes, just until softened and fragrant, then spoon them over and around the brisket in the crock pot.

In a bowl or large measuring cup, whisk together the BBQ sauce, beef broth, apple cider vinegar, brown sugar, and Worcestershire sauce until the mixture is smooth and combined.

Pour the BBQ sauce mixture evenly over the brisket and onions in the crock pot, making sure some liquid runs underneath the meat.

Cover the crock pot with the lid and cook the brisket on LOW for 8 hours, or until the meat is very tender and easily shreds with a fork.

When the brisket is done, transfer it to a large cutting board, let it rest for about 10 minutes, then use two forks to shred it into bite-sized pieces.

Skim any excess fat from the surface of the cooking liquid in the crock pot, then return the shredded brisket to the crock pot and gently toss it in the warm BBQ sauce and onions.

Warm the corn or flour tortillas in a dry skillet or wrapped in foil in a low oven until soft and pliable.

To assemble the tacos, place a portion of the shredded BBQ brisket onto each warm tortilla, then top with shredded green cabbage, crumbled queso fresco or mild feta, and chopped fresh cilantro.

Serve the tacos immediately with lime wedges on the side for squeezing over the filling just before eating.