Spray a frying pan with low-calorie cooking spray and set on a medium heat. Add the garlic, pepper, and half of the onion, then fry for 5 minutes. Dissolve the stock cube into the water, stirring to combine, then pour into the pan.
Fry for 5 minutes — the onions will be soft, and the liquid reduced to a glossy coating.
Add the pork mince and fry for 5 minutes, until browned on all sides. Add the BBQ seasoning, paprika, and garlic granules. Stir to coat the pork mince.
Add the chopped tomatoes, passata, sweetener, Henderson's relish, and tomato purée. Mix well and simmer for 10-15 minutes. It should be rich, reduced, and thick. Remember, this is served in a bun — so if the sauce is still runny, reduce it further.
To a bowl, add the carrot, gherkins, and remaining onion. Pour over the pickle juice and leave to one side while the pork mince finishes cooking.
Preheat the grill. Slice the buns down the middle and line up on the baking tray. Then spoon the pork mix into the buns and top with the grated cheese.
Place the tray under the grill for a few minutes until the cheese is melted. Serve with a little of the pickled slaw.