For the salad:
For the dressing:
Place the eggs in a large pan of water, bring up to the boil and then reduce to simmer for 7 minutes. Cool the eggs under running water and allow to cool completely before removing shell and cutting each in half, lengthways.
Whilst eggs are cooking, add the green beans to a pan of salted boiling water, bring back to the boil and then reduce to a simmer and cook for 6-8 minutes until just tender. Drain and place in ice water.
Season the tuna steaks all over with salt and pepper and cook for 2 minutes on each side on a grill pan, on a high heat. Set aside.
In a large bowl, combine the lettuce, green beans, cherry tomatoes and potatoes. Add the olives, then half the dressing, and toss to combine. Transfer the above to a serving platter, then arrange the hard-boiled eggs over top. Flake or slice the tuna and arrange this across the salad. Drizzle over the remaining dressing.