Using a bread knife, cut each slice of bread into 4 small rectangles about 1 inch thick.
Arrange the bread squares on a baking sheet and toast in a preheated oven at 180°C (350°F) for 8-10 minutes, until they are golden around the edges and slightly crisp.
While the bread cools slightly, toast the panko breadcrumbs in a skillet over medium heat with a tablespoon of butter until golden and crunchy, about 3-4 minutes. Stir frequently to prevent burning.
Spread a thin layer of mayonnaise on each toasted bread square, using a spoon or piping bag for neatness.
Layer slices of smoked turkey on top of the spread, pressing gently to adhere.
Place a small slice of Swiss cheese or a dollop of cream cheese on each sandwich for added richness.
Sprinkle the toasted panko breadcrumbs generously over each assembled bite while they are still warm, pressing lightly to help them stick.
Transfer the assembled bites to a wire rack and let rest for 2 minutes to set the topping and keep them crisp.
Garnish with chopped fresh dill and serve immediately to enjoy the contrast of tender bread and crunchy topping.