USE THIN SLICING DISC. Stand cucumbers in feed tube and slice, using medium pressure. Repeat until all cucumbers are sliced. Put cucumber slices, onion and rice vinegar in large mixing bowl. Toss well. Cover. Refrigerate from 4-8 hours. To serve, drain cucumbers. Toss with oil. Adjust salt and pepper. Arrange watercress leaves in wreath design on serving plates. Arrange cucumbers in center, dividing evenly. Garnish with chives. Serve.
NOTE: Seasoned rice vinegar, available in the Oriental section of most super- markets, is a blend of mild rice vinegar with a perfect balance of sugar, salt and water. If you are using rice vinegar, adjust the salt, sugar and water to taste.