Arrange the lettuce on a large platter or bowl, or divide between 4 large plates.
Cut the oranges into ¼-inch thick round slices and carefully pop out any seeds.
Arrange the oranges, avocados and red onion in and around the lettuce and season with salt and pepper.
Whisk together the ingredients for the vinaigrette, taste and adjust salt and pepper as needed.
Serve the vinaigrette on the side or drizzled on top of the salad.
