Line six small salad bowls (preferably glass) with lettuce leaves; break the remaining lettuce into bite-size pieces, dividing among the bowls. Arrange avocado slices, orange sections, grapefruit sections and onion rings on top of the lettuce in each bowl. Sprinkle each with about 1 tablespoon of Celery Seed Dressing and pass extra dressing when serving the salads.
Celery Seed Dressing
Combine all the ingredients in a jar with a tight-fitting lid and shake until well blended.