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

In a small bowl, combine the kosher salt, black pepper, smoked paprika, ground cumin, garlic powder, onion powder, and dried oregano to make a spice rub.

Rub the olive oil all over the brisket, then coat it evenly with the spice mixture, pressing it into the meat on all sides.

Place the thinly sliced onion and minced garlic in the bottom of a slow cooker or heavy oven-safe pot, spreading them into an even layer.

In a separate bowl, whisk together the beef broth, apple cider vinegar, tomato paste, and brown sugar until well combined.

Place the seasoned brisket on top of the onion and garlic, then pour the broth mixture around the sides of the meat, avoiding rinsing off the spice rub.

Cover and cook on low in a slow cooker for about 8 hours, or in a 300°F (150°C) oven for about 4 hours, until the brisket is very tender and shreds easily with a fork.

Once the brisket is cooked, transfer it to a cutting board and let it rest for about 10 minutes, then use two forks to shred the meat into bite-sized pieces.

Skim excess fat from the cooking liquid, then return the shredded brisket to the pot and toss it with some of the juices to keep it moist and flavorful.

While the brisket cooks or rests, prepare the cole slaw by adding the shredded green cabbage, shredded red cabbage, and grated carrot to a large mixing bowl.

In a separate bowl, whisk together the mayonnaise, sour cream, fresh lime juice, honey, kosher salt for slaw, and black pepper for slaw until smooth and creamy.

Pour the dressing over the cabbage mixture and toss well until all of the vegetables are evenly coated, then fold in the chopped fresh cilantro.

Taste the cole slaw and adjust the seasoning with a little more salt, pepper, or lime juice if needed, then refrigerate it for at least 20 minutes to let the flavors meld.

When you are ready to serve, warm the corn or flour tortillas in a dry skillet, on a griddle, or directly over a gas flame until soft and pliable.

To assemble the tacos, place a generous spoonful of shredded brisket onto each warm tortilla, top with a mound of cole slaw, and serve with lime wedges on the side for squeezing over the top.