Preheat the barbecue for medium heat and spray grates with nonstick cooking spray.
In a bowl mix together the beef mince, pork mince, bread crumbs, onion, egg, Worcestershire sauce, garlic, tarragon, sea salt and black pepper. Divide the mixture in half and form 2 loaves, each about 10cm in diameter and 15cm long. In a small bowl mix the barbecue sauce with tomato sauce until well combined.
Place each meatloaf directly on the barbecue then spread each with about 3 tablespoons of barbecue sauce mixture; cook about 1 hour.