In a small bowl, whisk all ingredients together until smooth. Refrigerate until well chilled.
ASSEMBLE THE SANDWICHES:
Spread all 8 slices of the toasted bread with mayonnaise (amount is your preference). Layer bacon, tomato and greens on 4 slices. Top with another slice of toasted bread.
Cut into halves and serve.
Notes
To vary the flavor, try using different types of bacon: smoked, honey-cured, etc., and different types of bread.