1. Preheat the oven to 400°F Lightly oil the potatoes and place in a baking tray, bake for 40 mins or until crisp and tender. If you're short on time, simply boil them for 15 mins instead. Once the potatoes are cooked, cut them in half.
Whilst the potatoes are cooking, blanch the beans in boiling water for 3 mins then drain and rinse in cold water.
Place the eggs in a small pan, cover with cold water, bring to the boil and simmer for 6 minutes Remove from the heat, drain, then rinse in cold water. Tap the shells all over and remove. Cut each egg in half and halve them again.Whisk all the dressing ingredients together and season to taste.
Heat a large non-stick frying or griddle pan until hot. Brush the tuna with a little oil then add to the pan and sear for 2-3 mins on each side, depending on how pink you like your tuna. Set aside to rest.
Empty the salad leaves into a large bowl and add the scallions, olives, cooled green beans and half of the dressing.
Divide the mixture between four plates, scatter over the halved potatoes, quartered eggs and finally lay the tuna on top.
To finish, drizzle a little of the remaining dressing over the tuna steaks and serve.