In a large saucepan or 4-quart Dutch oven, place unpeeled potatoes and a small amount of lightly salted water to cover. Bring to boiling; reduce heat. Simmer, covered, for 15 to 20 minutes or just till tender. Drain well; cool slightly. Peel, halve and cut potatoes into 1/4-inch slices.
In a large bowl, place potato slices. Sprinkle with vinegar, 1 teaspoon salt and black pepper; toss lightly to coat. Add green onion, parsley and garlic. Drizzle potato mixture with oil. Toss again lightly to coat. Cover; let stand at room temperature till ready to serve or store in refrigerator. Stir gently before serving. Makes 6 to 8 servings.