All the classic Niçoise flavors on one giant charcuterie platter. It's more assembly than actual cooking! Fresh, flavorful, and perfect for entertaining. If serving buffet style, you can make smaller platters and refill as necessary.
In a medium bowl, combine the vinegar, mustard, and salt and pepper to taste (I like 1/2 teaspoon each). Whisk in the olive oil to make an emulsion. If desired, blend with an immersion or regular blender (this makes the dressing lighter and frothier).
Add cooked potatoes to a medium bowl and drizzle with 3 tablespoons vinaigrette. Toss to coat.
Place the tuna in a bowl in the center of a large platter. Arrange the green beans, dressed potatoes, tomatoes, eggs, olives, watercress, and crackers or bread around the platter.
Drizzle 1/4 cup vinaigrette over the whole platter, including the tuna, reserving the remainder on the side for use. Garnish the potatoes with fresh dill. Garnish the whole platter with additional salt and pepper to taste.