Preheat oven to 350°F.
Spread 1 tablespoon of whole grain mustard on each slice of potato bread.
Note: you can also substitute horseradish spread for the whole grain mustard.
Top each slice of bread with the pastrami and cheese.
Bake open-faced sandwiches in oven for 4-5 minutes until cheese is warm and slightly melted.
Remove sandwiches from oven and top with sliced tomatoes, onions, cornichons, and mixed salad greens.
Serve open-faced, handheld or with a fork and knife. Enjoy!