Step 1

Combine the white wine vinegar, Dijon mustard, onion powder, salt and pepper in a small bowl. Add the olive oil in a slow, steady stream, whisking as you go. Set the dressing aside on the counter if you're making the salad within the next hour or so. Otherwise, store the dressing in the refrigerator and let it come to room temperature before using. Editor's Tip: Homemade salad dressings are good for up to two weeks in the fridge, so feel free to make it in advance. The oil and vinegar will separate, so re-whisk the mixture or give it a firm shake to reincorporate the ingredients.

Step 2

The easiest way to cook the vegetables for this dish is on the stovetop. For the potatoes, place the whole red potatoes in a small saucepan and cover them with cold water. Bring the water to a boil. Then, reduce the heat to a simmer and cover the pot. Cook until the potatoes are tender, about 15 to 20 minutes. Drain and discard the cooking water and let the potatoes cool before cutting them into quarters. For the green beans, blanching is best. Bring a small saucepan of salted water to a boil. When the water is boiling, add the green beans and cook for about 3 minutes, until they're tender-crisp. Remove the beans to a bowl of ice water to cool them down. Editor's Tip: This part can be done in advance to make prep easier! Store the cooked potatoes and green beans in the refrigerator for up to two days before assembling the salad.

Step 3

With all the components prepared, this step is easy. Divide the lettuce between two salad bowls. Top each plate with half of the potatoes, beans, tomatoes, olives, hard-boiled eggs and tuna. Drizzle the salads with dressing and serve any extra dressing on the side.