Add the potatoes to a large saucepan and cover with cold water. Add 1 tablespoon salt and bring to a boil. Cook until the potatoes are almost tender, 10 to 12 minutes. Remove to a bowl and set aside.
Meanwhile, bring a medium pot of water to a boil. Set up a large bowl of ice water and line a sheet tray with a paper towel or kitchen towel. Generously season the boiling water with salt. Add the green beans and cook for 2 to 3 minutes. Remove with a spider or drain in a colander and transfer to the ice bath. Once cooled, transfer the green beans to the lined sheet tray and pat dry.
On a large platter or low bowl, arrange the Bibb lettuce, potatoes, grape tomatoes, green beans, eggs, olives and tuna.
Whisk together the vinegar and Dijon with a little salt and pepper in a small bowl or measuring cup. Slowly stream in the oil while whisking until it is all combined and emulsified. Pour about half of the dressing over the salad, reserving the remaining dressing for serving. Serve with crusty French bread, if desired.
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