Place on parchment-lined sheet pans. Heat in preheated conventional oven at 350 degrees F for 30 to 35 minutes or until chicken is no longer pink (or heat in preheated convection oven at 325 degrees F for 25 to 30 minutes. Remove from oven. Keep warm above 140 degrees F.

 

Combine mayonaise and mustard in bowl and mix thoroughly. Cover and chill to hold. To assemble single serving: place 1 bun on flat work surface, grilled sides up. Spread 1/2 Tbsp mayonnaise mixture on each half. Layer bottom half of bun with 1 lettuce leaf and 3 tomato slices. Slice 1 chicken cordon bleu into 4 slices and shingle over tomatoes. Close sandwich with top half of bun and slice in half diagonally. Arrange on plate. 

 

Garnish plate with 1 parsley sprig and serve with coleslaw.