1in a small bowl,combine the 1st 6 ingredients; spread 1/2 over 2 slices of sourdough bread slices.
Layer with chicken,bacon,mozzarella cheese,onion, and tomato.
Spread remaining mayonnaise mixture over the remaining bread slices; put on top.
Brush outsides of sandwiches with butter.
2Cook on a panini grill or a George Foreman grill or a indoor grill for 3-4 minutes or until bread is browned and cheese is melted.