Season the chicken with the salt, garlic powder and black pepper and put it in a 6-quart slow cooker.
Add the onion, broth and Worcestershire, cover and cook on low for 2 1/2 hours.
Add both bell peppers and continue cooking until the chicken reaches at least 165°F and pulls apart, 1 1/2 to 2 hours.
Move the chicken to a board, slice or pull it into bite-size pieces and return it to the vegetables.
Use a slotted spoon to divide the chicken mixture among the hoagie rolls and top each with provolone.
Broil the open sandwiches until the cheese melts and the roll edges toast, 2 to 3 minutes.