Bring a large pan of water to the boil. Add the sliced potatoes and the eggs, and cook for 7 minutes.
Scoop the eggs out of the pan and set aside, tip in the green beans and cook for a further 4 minutes.
Drain the potatoes and beans and put with the eggs in a colander under cold running water until cool. Leave to dry.
Next, 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 tablespoon of cold water in a bowl until smooth. Season with black pepper and mix in the capers. Drizzle this dressing over the salad and serve.
*All information included in this recipe has been provided by Cornish Kings potatoes.