For dressing
1/4 cup Champagne vinegar
2 teaspoons Dijon mustard
2 large garlic cloves, minced
1/2 teaspoon sugar
1/3 cup extra-virgin olive oil
For salad
1 pound green beans, trimmed and halved
1 pound small (1- to 2-inch) yellow-fleshed potatoes such as Yukon Gold
2 (6-ounce) cans tuna in olive oil, drained
12 ounces cherry tomatoes, halved
1/2 cup pitted Kalamata olives (3 ounces)
3 tablespoons rinsed drained bottled capers (1 ounces)
1/2 cup finely chopped flat-leaf parsley
4 hard-boiled large eggs, quartered