Preheat a panini grill or a George Foreman grill and lightly grease it with non-stick spray (or preheat an oven to 350°F).
In a bowl mix the mayo and mustard. Spread the mixture onto each quartered piece of flatbread with a slice of cheese on each. Place the ham and pickles on and close up the sandwich.
Place on a panini grill or George Foreman grill and press down. Cook until the cheese is melted and bread is crispy. (If using an oven, place the sandwich on a baking sheet and cook until the cheese is melted.)