Blend the tuna, shallot, egg white, breadcrumbs, mint and cumin in a food processor until well combined. Season with salt and freshly ground black pepper.
Turn the mixture out into a bowl and shape into four equal-sized burgers. Chill in the fridge for 20 minutes.
Meanwhile, for the Niçoise-style salad, whisk the oil and vinegar together in a large bowl; add the remaining salad ingredients and mix until well combined. Season, to taste, with salt and freshly ground black pepper.
When the burgers have chilled, heat the oil in a frying pan and fry the burgers for three minutes on each side, or until cooked to your liking.
To serve, spread a little mayonnaise onto each ciabatta bun half and sandwich the burgers between them. Spoon the salad alongside. Serve with the lemon wedges.
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