Pick the herb leaves, trim and roughly chop the spring onions and chilli (deseed if you like) and finely grate the lemon zest, then place into a food processor.
Roughly chop the tuna and add to the processor with the ground coriander, then pulse until fairly fine (or finely chop and mix by hand).
Divide into 4, shape and squash into patties, then chill in the fridge for at least 30 minutes to firm up.
Preheat your barbecue or griddle pan to high. Brush the burgers all over with a little oil and season lightly with sea salt and black pepper.
Grill the burgers for 2 minutes on each side, or until cooked to your liking – the cooking time will depend on how thick you make them. It's OK to eat them when they're still a little pink inside, but if you want to cook them through, go ahead.
Trim and separate the lettuce leaves, and slice the tomatoes into rounds.
Halve the ciabatta rolls or burger buns, then toast the lightly on the barbecue or griddle.
To assemble, place a hot tuna pattie into the toasted roll or bun, then layer up with some lettuce leaves, rocket and sliced tomato. Cut the zested lemon into wedges for squeezing over, then serve with ketchup or salsa verde.
Make sure your barbecue or griddle pan is nice and hot before you cook the burgers!