In 4-quart saucepan, cook pasta as directed on package, adding potatoes and frozen green beans during last 5 to 7 minutes of cooking time; cook until vegetables and pasta are tender. Drain.
In large bowl, gently toss cooked pasta, potatoes and green beans with oil. Refrigerate until chilled, about 1 hour 30 minutes.
Stir in tuna, tomato and onions. Pour dressing over salad; stir gently to coat. Top with hard-cooked eggs.