Set up your barbecue for the heat canyon technique (place the coals on opposite sides of the barbecue to make two heat walls – this will create sections of hot, direct heat on the sides, with an indirect, cooler area in the middle to ensure your meat gets consistent heat throughout the cook). Place a drip tray inside the middle of the barbecue. Cover with the lid and allow to heat up like an outdoor oven – you want a temperature of around 160°C/320°F.
To make your sauce, combine the BBQ sauce and ketchup with a few drops each of Tabasco and chilli sauce, then set aside. Finely dice the onion, pepper and carrot, then put into a large bowl with all the mince, the garlic, bay, Worcestershire sauce, breadcrumbs, salt and pepper. Beat the eggs and add to the mixture, then use your hands to scrunch and mix it all together. Grate in half the cheese (if using), and scrunch to combine.
Remove the mixture to a clean work surface and shape into a rectangular loaf (roughly 25cm in length). Using the handle of a wooden spoon, make four diagonal indents (roughly 1cm deep) into the top of the loaf at 3cm intervals, then pour over half the sauce. Place the meatloaf on a big piece of tin foil or in an old roasting tray, then place on the middle of the barbecue. Cover with the lid and cook for 1 hour to 1 hour 15 minutes, or until cooked through. Grate and sprinkle over the remaining cheese (if using), and continue cooking for a minute or so with the lid on, until melted. Remove to a board to rest for around 10 minutes, then slice it up and serve drizzled with the remaining sauce. Cheers, Grandma!