1 Peel avocados, halve, and remove pits. Dip avocados into an ascorbic-acid solution such as used for preserving fruits. Or sprinkle with fresh lemon or lime juice.
2 Peel oranges or grapefruit and onion. Cut oranges and onion into thin slices. For grapefruit, slice each section away from the membrane and remove. Separate onion slices into rings.
3 Place the lettuce leaves on salad plates. Arrange avocado slices with orange slices or grapefruit sections on lettuce. Top with onion rings. Drizzle with dressing.