Bring a large pot of water to boil. While you're waiting for the water to boil, start making the vinaigrette.
To make the vinaigrette, dissolve the salt in the vinegar first by whisking it with a fork in a small bowl, or by shaking the salt and vinegar together in a small mason jar. This is essential to avoid a gritty texture in your vinaigrette. If you add the salt later it will remain as speckles in your vinaigrette. Add all of the rest of the vinaigrette ingredients to the mixture and whisk/shake until everything is well combined. Set aside.
Once your water has come to a boil, add the baby potatoes into the pot.
While the potatoes are boiling, wash and chop the romaine and add it to a large salad bowl.
After the potatoes have boiled for 15 minutes. Add the eggs to the pot. After an additional 3 minutes, add in the green beans to blanche them. Continue boiling everything for an another 3 minutes. Turn off the heat.
At this point, the potatoes have boiled for about 26 minutes, the eggs for 6 minutes, and the green beans for 3 minutes. Ladle out the hard boiled eggs and place them in a small bowl of ice water. Pour the rest of the pot contents out over a colander, and run cold water over them. Once the potatoes cool, slice them in half. Peel the eggs and slice in half.
To assemble: Place the halved potatoes, green beans, eggs, olives, and capers over the lettuce. Sprinkle the chopped dill over the salad and top with salmon or tuna if using. Drizzle the vinaigrette over the whole thing. Bon Appétit!