Cut the bread into small cubes and lightly toast in the pan without fat. Put aside. Clean the spring onions, wash them and cut into fine rings. Wash tomatoes, peppers and cucumber and cut into small cubes. Mix salt / pepper with vinegar and oil and pour over the vegetables, mix and let steep for at least 30 minutes. Before serving, add the bread cubes and tuna and fold in. Serve sprinkled with capers.