Preheat the oven to 450 degrees F (230 degrees C). Divide quartered bread slices evenly between 2 large baking sheets . Combine ham, Swiss cheese, mustard, and mayonnaise in a large bowl and mix well. Place 1 tablespoon of mixture on top of each piece of bread on 1 of the baking sheets. Bake topped bread in the preheated oven for 4 minutes. Add baking sheet with plain bread to the oven and continue baking 3 minutes more. Remove both baking sheets from the oven. Place a dill pickle slice on each topped bread slice; cover with a piece of plain toasted bread. Secure each mini sandwich with a toothpick.