Put potatoes in a medium saucepan; cover with cold water and season with salt. Bring to a simmer over medium-high heat and cook until fork-tender, about 5 minutes. Drain and transfer to a medium bowl; drizzle with ¼ cup vinaigrette and let cool.While potatoes are cooking, make the vinaigrette by whisking all vinaigrette ingredients together in a small jar or bowl. I find it easiest to mix up dressings in a small jar and then shake the jar to combine all ingredients. Also, cut tomatoes and toss in a small bowl with salt and pepper. Chop eggs and radishes. Set all aside.Bring a separate saucepan of salted water to a boil. Fill a bowl with salted ice water. Add the green beans to the boiling water; cook until crisp-tender and bright green, 3 minutes. Drain and immediately plunge into the ice water to cool; drain and pat dry.Divide lettuce among 4 plates. Arrange the potatoes, tomatoes, eggs, radishes, green beans and tuna on top. Drizzle with dressing and top with the olives.