Spread mustard evenly over cut sides of bread. Arrange half of cheese and half of ham on bottom half of loaf; top with pickle slices. Repeat layer with remaining cheese and ham; cover with top half of loaf. Cut into quarters.
Heat a large, heavy skillet coated with cooking spray over medium-high heat. Add sandwiches; press with a heavy skillet (such as cast iron). Cook 2 minutes on each side.