Stir together first 6 ingredients. Spread half of mixture evenly on half of white bread slices; top with remaining half of white bread slices. Spread remaining half of mixture evenly on half of wheat bread slices; top with remaining half of wheat bread slices. Remove crusts with a serrated knife; cut each sandwich into 4 squares. Arrange, stacked in pairs, on a serving plate in a checkerboard pattern, alternating white and wheat. Garnish, if desired.
Note: For testing purposes only, we used Pepperidge Farm Very Thin White and Wheat Bread.