Heat the oven to 400°F. Heat the butter and oil in a 12-inch skillet over medium heat. Add the green onions and garlic and cook until the onions are tender. Stir in the broth, artichokes, mushrooms, parsley and black pepper and heat to a boil.
Remove the skillet from the heat. Add the stuffing and mix lightly.
Spoon 3 cups stuffing mixture down the center of the pork. Fold the sides over the filling to form a roll. Tie the pork crosswise at 2-inch intervals with kitchen twine.
Season the pork with additional black pepper and the garlic powder. Place the pork into a large roasting pan.
Bake for 45 minutes or until the pork is cooked through. Let the pork stand for 10 minutes. Remove the twine before slicing.