- Bring a large pan of water to the boil. Add the potatoes and the eggs, and cook for 7 mins. Scoop the eggs out of the pan, tip in the green beans and cook for a further 4 mins.
- Drain the potatoes, beans and eggs in a colander under cold running water until cool. Leave to dry.
- Peel the eggs and cut into quarters. Arrange the lettuce leaves in 2 shallow bowls. Scatter over the beans, potatoes, tomatoes and egg quarters. Pat the anchovies with kitchen paper to absorb the excess oil and place on top.
- Flake the tuna into chunks and scatter over the salad. Mix the mayonnaise and 1 tbsp cold water in a bowl until smooth. Drizzle over the salad and serve.