Make the dressing by whisking together the mustard, honey, vinegar, and oil, until smooth. Season with salt and pepper.

Heat a large pan over medium-high heat. Add the ham and cook 3-4 minutes on each side, or until browned and heated through. Remove from the pan and set aside.

Return the pan to the stove and add the butter. When the butter is melted, add the pretzel pieces. Cook 5-8 minutes, or until deeply toasted. Remove from heat.

Arrange the lettuce in a large serving bowl. Top with the ham, pretzel croutons, apples, and cheese. Serve with the honey mustard.