Spread half the mayonnaise on 2 bread slices. Layer with the avocado, 2 tomato slices and 1 lettuce leaf. Spread 2 bread slices with the remaining mayonnaise. Place, mayonnaise-side up, on the sandwiches. Layer with the cucumber, remaining tomato slices and lettuce. Top with the remaining bread slices.
Tip: This recipe can be halved to make 1 serving.