To Make Stuffed Burgers: Place ground meat in a large bowl & combine with spices. Mix well. Shape into 8 thin patties. Divide onion/apple mixture into 8 portions. Place one portion on each of 4 patties ( reserve other 4 portions for later use). Top with remaining 4 patties & press gently to seal enclosing filling completely. Place burgers on preheated, greased barbecue grill over medium heat, close lid & grill, turning once. Cook approximately 14 minutes total. Top with remaining onion/apple mixture. Serve on buttered, lightly grilled Ciabatta buns.