Whizz the tuna, basil, mint, spring onions, coriander and lemon zest and red chilli, if using, together in a food processor or, alternatively, chop them all up together finely with a big chopping knife. Tip the mixture out on to a clean work surface and divide into four equal pieces.

Wet your hands (so the tuna won't stick to them) and shape the lumps of tuna – first into balls, then into burgers by patting them down with the palm of your hand. Chill the burgers for at least half an hour to let them set.

Heat a barbecue or griddle pan until hot. Brush the burgers on each side with a little oil and season with a little salt and pepper. Grill for 2 minutes on each side or until cooked through – the cooking will depend on how thick you made your burgers. It's OK to eat them when they're still a little pink inside, but if you want to cook them through then go ahead.

Toast your buns lightly on the hot griddle pan or barbecue and make the burgers by filling each bun with a hot tuna pattie, some dressed salad leaves, some sliced tomato, a wedge of lemon on the side and some ketchup.