Season the chuck roast on all sides with salt, pepper, smoked paprika, onion powder, and garlic powder. Pat dry first for better searing.
Sear the beef in olive oil over medium-high heat for 3 to 4 minutes per side until deeply browned. Transfer to slow cooker or Dutch oven.
Add sliced onion, minced garlic, beef broth, tomato paste, Worcestershire sauce, and dried thyme around the beef.
Cook on LOW for 8 hours or HIGH for 5 hours in the slow cooker. For oven method, cover and cook at 300°F for 3.5 to 4 hours.
Shred the beef using two forks, then return it to the pot and stir into the cooking juices. Rest for 5 minutes.
Build the sandwiches on toasted buns and top with pickles, coleslaw, or cheese as desired.