Arrange potatoes and carrots around outer edge in 4- to 6-quart slow cooker.
If pork roast comes in netting or is tied, do not remove. Mix mustard, rosemary, thyme, salt and pepper in small bowl; spread evenly over pork. Place pork in slow cooker (it will overlap vegetables slightly). Sprinkle onion over pork. Pour broth evenly over pork and vegetables.
Cover and cook on Low heat setting 8 to 9 hours.
Remove pork and vegetables from cooker, using slotted spoon. Place pork on cutting board; remove netting or strings. Slice pork. To serve, spoon juices from cooker over pork and vegetables.