Drain the tuna and tip it into a large bowl. Rinse the beans under cold running water, drain and add to the tuna together with the tomatoes, cut into chunks, sliced radishes, finely chopped onions and parsley.
Whisk all marinade ingredients in a small bowl until blended. Pour over the salad and stir in with your hands.
Half the ciabatta rolls lengthways, brush with olive oil and fry in a hot griddle pan until golden brown.
Thinly spread the sundried tomato paste over the ciabatta and pile the salad on top.