Preheat oven to 400°F (200°C). Toss asparagus with olive oil, salt, and pepper, then roast for 10–12 minutes until tender.
Boil potatoes in salted water for 10–12 minutes until fork-tender. Drain and set aside.
Bring a small pot of water to a boil and cook eggs for 8–9 minutes. Transfer to ice water, peel, and halve.
Blanch green beans in boiling water for 2–3 minutes, then transfer to ice water to keep them crisp and vibrant.
Season tuna steaks with salt and pepper. Sear in a hot pan for 2–3 minutes per side for medium-rare, or cook to your preference. Slice into strips.
In a small bowl, whisk together all dressing ingredients until emulsified.
Assemble the salad: arrange greens on a large platter, then layer potatoes, roasted asparagus, green beans, cherry tomatoes, olives, eggs, and tuna.
Drizzle dressing over the salad just before serving. Toss lightly or serve composed.