Pour half of the Worcestershire sauce into the pan of a slow cooker, and half of the garlic pepper. Place the roast in the pan, and sprinkle remaining Worcestershire sauce and garlic pepper over the top. Add the onions, and chilies, and pour in the chicken broth. Cover, and cook on Low for 8 to 10 hours.
When the roast is tender enough to pull apart with a fork, add the green salsa, and the beans, if desired. Continue cooking until heated through. Serve as soup or over chimichangas.