Pre-heat the oven to 200°C/ 400°F/ Gas mark 6. Cook the potatoes and beans separately until just soft. Drain and set aside.
Flake the tuna fish into a bowl. Add the potatoes, green beans, black olives and capers and mix together. Place the ciabatta halves, facing upwards on a baking tray. Spread a thin layer of tomato and olive sauce on the base of the bread. Divide the mixture over the bread and top with sliced Parmesan cheese.
Bake for 10 minutes or until the cheese is bubbling. To serve, garnish with anchovy fillets.
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