In a covered large saucepan cook potatoes in a small amount of boiling, lightly salted water for 10 to 12 minutes or until tender, adding beans the last 3 to 5 minutes of cooking; drain. Rinse with cold water; drain again.
In a medium bowl stir together the oil, vinegar, rosemary, salt, and pepper. Add potato mixture and green onions; toss gently to coat. Makes 6 to 8 servings.