First cook the potatoes and beans separately in boiling salted water. Remove from pans, drain and cool. Heat oil in a pan and quickly sear tuna steaks for just about 1 minute each side. Reserve with potatoes and beans.
Halve cherry tomatoes and place in a bowl with hard boiled quail’s eggs. Cut anchovy fillets into strips and add. Halve any large baby potatoes but add all others whole, with black olives and beans. Break tuna into chunks and add with a handful of frilly leaves.
For the dressing, place Grey Poupon mustard in a bowl and whisk in white wine vinegar. Continue whisking in olive oil, then season with salt and freshly ground black pepper.
Pour over salad and sprinkle with parsley, toss with clean hands and serve on individual plates.