Directions

1. In a medium bowl, whisk together vinegar, mustard, shallot, 1 teaspoon salt, 1/2 teaspoon pepper, and sugar. Slowly whisk in oil until well combined; set dressing aside.
2. Prepare an ice-water bath and set aside. Bring a medium saucepan filled with water to a boil. Lightly salt water and return to a boil. Add green beans and cook until bright green and slightly tender, about 2 minutes. Drain and immediately transfer to ice-water bath. Drain and transfer to a large bowl. Add 1 tablespoon dressing and toss to coat; set aside.
3. Place potatoes in a medium saucepan with enough cold water to cover. Bring to a boil over high heat; immediately reduce to a simmer. Cook until potatoes are tender, about 15 minutes. Drain and let cool. Cut potatoes into 1-inch pieces and transfer to a medium bowl. Add 1 tablespoon dressing and toss to coat. Gently fold in capers, dill, and celery; season with salt and pepper and set aside.
4. Place eggs in a small saucepan with enough cold water to cover. Bring to a boil over medium-high heat; immediately cover and remove from heat. Let stand for 8 minutes. Drain and run eggs under cold, running water until cooled. Peel, halve lengthwise, and set aside.
5. Divide lettuce evenly between 4 plates. Arrange green beans, potato mixture, eggs, tomatoes, tuna, and olives over lettuce. Drizzle with remaining dressing and serve immediately.