Cover potatoes with cold water in a medium saucepan, season with salt and bring to a boil. Reduce heat to medium and cook until the potatoes are just tender, about 10 minutes. Drain. Let stand until cool enough to handle. Slice into a large bowl and toss with 1/4 cup dressing.
Cook green beans in boiling salted water until just tender, about 5 minutes. Drain, refresh under cold water and pat dry. Add to the potatoes along with another 1/4 cup dressing. Toss gently to coat.
Transfer to a platter or individual plates. Arrange tomatoes and eggs around the outside; scatter tuna, olives, onions, capers and parsley over the top. Arrange anchovies decoratively; drizzle with the remaining dressing.
Tip: To hard-boil eggs: Place eggs in a single layer in a saucepan; cover with water. Bring to a simmer over medium-high heat. Reduce heat to low and cook at the barest simmer for 10 minutes. Remove from heat, pour out hot water and cover the eggs with cold water. Let stand until cool enough to handle before peeling.
Note: Chunk light tuna, which comes from the smaller skipjack or yellowfin, has less mercury than canned white albacore tuna. The FDA/EPA advises that women who are or might become pregnant, nursing mothers and young children consume no more than 6 ounces of albacore a week; up to 12 ounces of canned light tuna is considered safe.
381 calories;14 g fat(3 g sat); 6 g fiber; 39 g carbohydrates; 26 g protein; 82 mcg folate; 173 mg cholesterol; 6 g sugars; 0 g added sugars; 1359 IU vitamin A; 40 mg vitamin C; 157 mg calcium; 4 mg iron; 750 mg sodium; 1094 mg potassium