How to Make It
Combine first 4 ingredients in a small bowl, stirring with a wire whisk. Arrange orange and onion in a 13- x 9- x 2-inch dish. Pour vinegar mixture over orange and onion. Cover and chill at least 30 minutes.
Place lettuce evenly on individual salad plates. Arrange orange and onion over lettuce, using a slotted spoon. Drizzle vinegar mixture evenly over salads.