Trim excess fat from the beef chuck roast and season with salt and pepper.

In a bowl, mix together BBQ sauce, beef broth or water, sliced onion, minced garlic, brown sugar, smoked paprika, and ground cumin.

Place the seasoned beef chuck roast into the slow cooker.

Pour the BBQ sauce mixture over the beef, ensuring it is well coated.

Cover and cook on low heat for 8-10 hours or on high heat for 4-5 hours, or until the beef is tender and easily shreds with a fork.

Once cooked, remove the beef from the slow cooker and shred it using two forks. If there's excess liquid, you can strain it or use a slotted spoon to transfer the beef to a bowl.

Heat the corn tortillas either in a dry skillet or microwave until warm and pliable.

Fill each tortilla with shredded BBQ beef and top with shredded cabbage or coleslaw mix.

Serve the tacos with lime wedges on the side for squeezing over the tacos. Garnish with fresh cilantro if desired.