Cut 1 large, crusty loaf lengthways into 3 x 1.5cm thick slices. Brush with olive oil and lightly grill all sides. Place 2 sliced tomatoes, 4 cooked crispy bacon rashers and 200g thinly sliced cooked chicken breast on a bread slice. Top with another bread slice, then top this slice with a spreading of mayonnaise, 200g thinly sliced cooked chicken breast and 4 butter lettuce leaves. Season and top with the third bread slice. Secure slices with 4 toothpicks and cut into quarters.