Put the chutney ingredients in a pan and simmer over a medium heat, stirring regularly for 25-30 minutes or until the tomatoes have broken down and the mixture has thickened and looks jammy. Remove from the heat, cool and season well.

Squash together the mince, egg, parsley, garlic granules and lemon zest with some seasoning using clean hands, then form into four burger patties. Heat the grill to its highest setting and move the rack to the upper third of the oven. Put the patties on a tray and cook under the hot grill for 4-6 minutes on each side, or until cooked through.

Toast the cut sides of the buns under the grill or in a dry frying pan. Spread with the mayonnaise, then sandwich with the lettuce, tomato and onion slices, burger patties and tomato chutney. Serve with a mixed salad, coleslaw or sweet potato wedges.