Marinate the Brisket: In a large bowl, combine olive oil, garlic powder, onion powder, smoked paprika, cumin, salt, pepper, apple cider vinegar, and water. Mix well and coat the brisket evenly. Secure the brisket in an airtight container and let it soak in the marinade in the refrigerator for at least 4 hours, though overnight marinating brings out even richer flavors.
Prepare for Slow Cooking: Preheat your oven to 150°C (300°F). Place the marinated brisket in a covered roasting pan. Cover tightly with foil to lock in moisture.
Slow-Cook the Brisket: Cook in the preheated oven for 3 hours, or until the meat is fork-tender. Occasionally baste the brisket with its own juices to keep it moist.
Shred the Meat: Remove the brisket from the oven and let it rest for 10 minutes. Then, shred the meat using two forks. Mix in a little of the remaining cooking liquid to retain flavor.
Assemble the Sliders: Lightly toast the slider buns. Spread a thin layer of avocado mayo on the buns. Add a generous serving of shredded brisket, top with shredded cheddar cheese, fresh lettuce, tomato slices, red onion, and pickles if using.
Serve and Enjoy: Serve immediately while warm. These sliders are perfect for a hearty meal or as an appetizing treat at gatherings.