For the vinaigrette, whisk lemon juice, oil, shallot, herbs and mustard in bowl. Season with salt and pepper and set aside. Arrange bed of lettuce on each plate. Place tuna in bowl and break it up with a fork. Add vinaigrette and stir to combine. Mound tuna in center of lettuce.
Toss tomatoes, red onion and three tablespoons of vinaigrette in bowl. Arrange tomato-onion mixture in a mound on the plate. Return water to boil and add one tablespoon salt and green beans. Cook until tender but crisp, three to five minutes. Drain beans and transfer to ice water until just cold. Dry beans with paper towel and toss with vinaigrette. Arrange on lettuce. Place hard-boiled eggs and olives on the lettuce. Serve immediately.