Start to cook the bacon so that it becomes crisp. In a blender or food processor puree the olives, mustard, anchovy paste, olive oil, vinegar, and garlic; season to taste with salt and pepper and adjust amount of vinegar for tang.
Toast the bread lightly. Remove bacon to paper towels to drain.
To assemble, spread each slice of bread with olive mixture, on one side only. Set some bacon on bottom of bread, then top with tomato and onion slices, chicken and cucumber; salt and pepper each layer lightly as you go. Top with bread, mayonnaise side down; repeat with second layer of fillings and finish with third slice of bread, olive mixture side down. Assemble the second sandwich in the same way.