Wash potatoes. Cook in boiling water to cover 20 to 25 minutes or until tender; drain and cool slightly. Cut each potato into 6 wedges. Set aside.
Snap off tough ends of asparagus. Remove scales from spears with a knife or vegetable peeler, if desired. Cut asparagus into 1-inch pieces. Arrange asparagus in a vegetable steamer over boiling water. Cover and steam 4 to 5 minutes or until crisp-tender. Rinse with cold water.
Combine potato wedges, asparagus, and green onions in a shallow dish. Combine vinegar and next 4 ingredients; pour over potato mixture, and toss gently. Cover and chill at least 1 hour, stirring occasionally. Spoon potato mixture evenly onto 2 lettuce-lined salad plates.