Place halved new potatoes in a medium pot and cover with cold water by 1 inch. Add 1/2 tsp salt. Bring to a boil over high heat, then reduce to a simmer and cook until tender when pierced with a knife, 10–12 minutes depending on size. Drain and let cool slightly; keep warm or set aside to cool for the salad.

Blanch green beans

While potatoes cook, bring a separate pot of salted water to a boil. Add trimmed green beans and blanch 2–3 minutes until bright green and just tender-crisp. Immediately transfer to an ice bath to stop cooking, then drain and pat dry. If beans are large, cut in half on the diagonal.

Eggs

Hard-cook eggs

Place eggs in a small pot and cover with cold water by 1 inch. Bring to a gentle boil, then cover, remove from heat and let stand 9–10 minutes. Transfer eggs to ice water for 5 minutes, peel, and halve lengthwise. Reserve for plating.

Dressing

In a small bowl or jar combine 4 tbs extra-virgin olive oil, 2 tbs fresh lemon juice, 1 tsp Dijon mustard, 1 tsp red wine vinegar, 1/2 tsp salt, and 1/2 tsp freshly ground black pepper. Whisk or shake vigorously until emulsified. Taste and adjust seasoning. Stir in chopped parsley and set aside.

Assemble salad

Toss the mixed salad greens lightly with about half of the dressing to coat (use more or less to taste) and arrange on a large platter or divide among 4 plates.

Slice or quarter the warm potatoes if large and scatter them over the greens along with the blanched green beans, tomatoes, olives, sliced shallot, and capers.

Flake the drained canned tuna into large chunks and distribute over the salad (or arrange seared tuna slices). Place the halved hard-cooked eggs on top.

Drizzle remaining dressing over the arranged salad and finish with a final 1–2 tbs extra-virgin olive oil if desired. Season with additional salt and pepper to taste.

Serve immediately as a composed Niçoise-style lunch for up to 4 people.