Add the roast. Place the chuck roast into the bottom of your slow cooker.
Build the sauce. Add the BBQ sauce, onion, garlic, Worcestershire sauce, green chilies, brown sugar, and half of the cooked bacon to the slow cooker.
Coat the roast. Mix everything together well until the roast is completely coated in the sauce mixture.
Slow cook. Cover and cook on low for 8 to 9 hours, or on high for 5 to 6 hours, until the beef is tender and shreds easily with a fork.
Shred the beef. Shred the beef directly inside the slow cooker with two forks, then stir it through the sauce so it soaks up all the juices.
Toast the onions. Heat a dry frying pan over medium heat and toast the crispy fried onions for 3 to 5 minutes, stirring occasionally, until golden and fragrant.
Fill the buns. Split the hamburger buns and toast them lightly if desired, then pile a generous amount of shredded beef onto the bottom half of each bun.
Assemble and serve. Top the beef with a slice of Cheddar, the reserved bacon, and the toasted crispy onions, then place the top bun on face-down and serve warm so the cheese melts.