Toast slices of bread on one side. Spread untoasted side of one slice with Mayonnaise Dressing, cover with lettuce leaf; add thinly sliced chicken, then more dressing and another leaf of lettuce. Put on thin, crisp slices of bacon, then sliced tomato and lettuce. Finish with second slice of toast, spread generously with dressing. Garnish with tiny lettuce leaves, and serve at once. The tomato may be omitted.