Prep and salt the water: Fill a medium saucepan with water and bring to a rolling boil. Add a generous pinch of salt (it should taste like the sea). Salting the water seasons the potatoes and green beans from the inside out as they cook.

Cook the potatoes: Add the whole small waxy potatoes to the boiling water and cook until just tender when pierced with a knife, about 12–15 minutes depending on size. Waxy potatoes hold their shape and have a creamy texture that is ideal for Niçoise. Drain, let cool slightly, then halve or thickly slice while still warm so they absorb a little of the dressing.

Blanch the green beans: While the potatoes are cooking, trim the green beans. When the potatoes have about 3 minutes left, add the green beans to the same boiling, salted water and cook for 2–3 minutes until bright green and just tender-crisp. Blanching in the same water both saves time and keeps maximum flavor. Immediately transfer the beans to an ice bath (or very cold running water) to stop cooking and preserve color and snap.

Make the lemon–olive oil dressing: In a small bowl or jar combine the extra-virgin olive oil, fresh lemon juice, Dijon mustard, minced garlic, a pinch of salt and several grinds of black pepper. Whisk or shake vigorously to emulsify — this binds the oil and acid so the dressing clings to the vegetables and tuna rather than running off.

Prepare the tuna: While the potatoes rest and beans chill, open and thoroughly drain the canned tuna. Flake gently with a fork into large pieces — leaving the tuna in larger flakes gives the salad a better mouthfeel and makes it more restaurant-style. Taste a small piece and add a pinch of salt only if needed (some canned tuna is already well-seasoned).

Assemble the salad: On a serving platter or individual plates, arrange the potato halves (warm), blanched green beans, halved cherry tomatoes and Kalamata olive halves. Nestle the flaked tuna on top or in the center. Drizzle the lemon–olive oil dressing over the potatoes first (warm potatoes absorb flavor), then lightly over the vegetables and tuna. Scatter chopped parsley for freshness.

Finish and serve: Let the salad sit for 2–3 minutes to allow flavors to marry, then taste and adjust with a final pinch of salt, more lemon, or extra-virgin olive oil if desired. Serve immediately — the contrast of warm potatoes and cool, crisp vegetables is part of what makes this version special.