Boil, steam or microwave potatoes until just tender, drain.
Place eggs in a small saucepan, cover with cold water and bring to the boil. Boil 5 minutes then drain and rinse under cold water. Peel shells from eggs and cut into halves. Place beans in a heatproof bowl. Cover with boiling water, stand 1 minute then drain, refresh under cold water and drain again.
To make croutons, cut bread into cubes or roughly tear into small pieces. Spread over a baking tray. Spray lightly with cooking oil. Cook under a preheated grill for 1-2 minutes or until golden. Set aside to cool.
To make dressing, combine oil, vinegar and mustard in a screw top jar. Season with pepper. Secure lid and shake well.
Divide lettuce leaves between 6 serving bowls, top with tuna, potatoes, eggs, beans, tomatoes and olives. Drizzle with dressing and sprinkle with croutons.