Stir together mayonnaise and yellow mustard in a small bowl. Spread mayonnaise mixture evenly onto 1 side of toasted bread slices. Layer 4 bread slices, mayonnaise sides up, with 1 slice ham, 1 slice turkey, 2 bacon slices, 1 Swiss cheese slice, 2 tomato slices, and 1/2 lettuce leaf. Top each with 1 bread slice, mayonnaise side down; layer with remaining ham, turkey, bacon, cheese, and lettuce. Top with remaining 4 bread slices, mayonnaise sides down. Cut each sandwich into quarters, and, if desired, secure with wooden picks.
Note: For testing purposes only, we used Pepperidge Farm Sourdough Bread.