Trim fat from chops. In a large skillet, heat oil over medium heat. Add chops; cook until browned, turning to brown evenly. Drain off fat. Place onion in a 3-1/2- or 4-quart slow cooker (see Tips). Add chops. Using a mortar and pestle, crush tapioca. In a medium bowl, combine tapioca, mushroom soup, apple juice, Worcestershire sauce, snipped or dried thyme, and garlic powder; stir in mushrooms. Pour over chops in slow cooker.