Pat the beef dry with paper towels. Season the chuck roast generously on all sides with salt, pepper, garlic powder, onion powder, and dried thyme, pressing the spices into the meat. Optional: Heat 1 to 2 tablespoons of oil in a large skillet over high heat and sear the roast for 2 to 3 minutes per side until browned.

Layer the sliced onions at the bottom of your slow cooker, then place the seasoned roast on top. Pour in the beef broth, Worcestershire sauce, and soy sauce around the meat. The liquid should come about halfway up the sides of the roast.

Cover and cook on low for 7 to 8 hours or on high for 4 to 5 hours until beef is fork-tender and reaches at least 190°F internal temperature. Avoid lifting the lid during cooking.

Transfer the cooked beef to a cutting board and shred into bite-sized pieces using two forks, pulling the meat apart along the grain. Return shredded beef to the slow cooker and let it soak in the juices for 10 minutes.

While the beef rests, toast the hoagie rolls cut-side up under the broiler for 1 to 2 minutes until golden and lightly crispy around the edges. Watch closely to prevent burning.

Using tongs, pile generous amounts of shredded beef onto each toasted roll, letting excess liquid drip back into the pot for a few seconds. Top with a slice of provolone cheese and return to the broiler for 1 to 2 minutes until cheese is melted and bubbling.

Strain the cooking liquid through a fine-mesh strainer to remove onions (save these caramelized onions if desired for topping). Pour the au jus into small bowls for serving alongside each sandwich.