Place the chuck roast in a roasting pan (or sturdy disposable foil pan) and coat it on all sides with the Worcestershire sauce. Season it generously with Traeger Prime Rib Rub.
When ready to cook, start the Traeger grill on Smoke with the lid open until the fire is established (4 to 5 minutes).
Remove the meat from the roasting pan and place it directly on the grill grate. Smoke for 1 hour. Set the roasting pan aside; you will need it later.
Meanwhile, in a large saucepan or frying pan, saut the onions, bell pepper, poblano pepper, jalapeno, and garlic in the oil over medium heat until softened, about 5 minutes. Add the tomatoes, beef broth, lime juice, chili powder, cumin, oregano, and salt and pepper and bring to a boil over high heat.
Reduce heat, and simmer the tomato mixture for 20 minutes. Taste for seasoning, adding more chili powder, cumin, or salt and pepper as needed. Transfer the smoked chuck roast to the reserved roasting pan.
Increase the temperature of the Traeger to 300F.
Slice the roast into 4 or 5 chunks of roughly equal size. Carefully pour the hot tomato mixture over the meat and cover it tightly with a lid or heavy duty foil.
Place the roasting pan on the grill grate. Roast the meat for 2-1/2 to 3 hours, turning the meat chunks over in the juices once or twice. (Use tongs to lift the lid or foil to avoid steam burns.) If the pan seems dry, add more beef broth. The meat is done when it is very tender and can be pulled apart easily.
Let the meat cool slightly, then shred with a pair of forks. If not serving immediately, return to the tomato mixture, cool, cover, and refrigerate. (Machaca can be made up to 3 days ahead.)