Mix brown sugar and seasonings in small bowl. Reserve 2 tablespoons. Toss sweet potatoes, onions and butter in medium bowl. Add remaining seasoning mixture; toss to coat well. Spread in large, shallow, foil-lined baking pan sprayed with no stick cooking spray.
Roast in preheated 375ºF oven 10 minutes. Rub pork tenderloin with reserved seasoning mixture. Push sweet potatoes and onions to one side of pan. Place pork tenderloin on other side.
Roast 25 minutes or until pork is desired doneness and sweet potatoes are tender. Slice pork and serve with sweet potatoes and onions.