Pat the beef brisket dry with paper towels. Season evenly with salt, black pepper, chili powder, smoked paprika, cumin, and oregano.

Heat olive oil in a Dutch oven over medium-high heat. Sear the brisket for about 4–5 minutes per side until a deep golden crust forms. Remove and set aside.

In the same pot, cook sliced onions for about 5 minutes until soft. Add garlic and cook until fragrant. Stir in tomato paste and cook for 1 minute.

Pour in beef broth, lime juice, and apple cider vinegar. Scrape the bottom of the pot to release browned bits.

Return brisket to the pot. Cover and cook on low heat for 3–3½ hours until the meat becomes fork-tender.

Remove brisket and shred it using two forks. Return shredded meat to the cooking juices and simmer for 10 minutes.

Heat a skillet over medium heat and cook portions of the shredded brisket until edges become slightly crispy.

Warm corn tortillas in a dry skillet for about 30 seconds per side.

Assemble tacos by filling tortillas with brisket and topping with diced onion, cilantro, avocado, queso fresco, and lime juice.