Spread 2 slices of bread with the mustard. Layer each with 3 slices of ham, half of the pear slices, a dash of pepper and 1/2 cup mozzarella cheese. Top with remaining bread. Lightly spread margarine on the outer sides of each sandwich.
Heat a frypan over medium heat. Grill the sandwiches until the cheese is melted and the bread is golden brown, about 3 minutes per side. Cut each sandwich in half to serve.