Preheat oven to 450°F and position rack to the lowest setting. Stretch pizza dough to fit in a greased 11 x 17-inch rimmed baking sheet.
Measure out 1 tablespoon dressing and set aside. Spread remaining dressing all over dough, leaving a ½-inch border. Place sliced mozzarella and pear slices over dough; sprinkle with walnuts.
Bake for 15 to 18 minutes or until golden brown on the bottom. Scatter prosciutto ribbons all over pizza. Toss arugula with reserved dressing; sprinkle over pizza. Serve immediately.
