- Prepare a hot fire in a grill and preheat a pizza stone for at least 30 minutes, until the thermometer on the stone registers 500°F.
- Using a rolling pin or your hands, gently roll out or stretch the dough into a 10-inch round. Lightly dust a pizza peel with flour and lay the dough on top. Lightly brush the dough with olive oil. Scatter the onion over the dough and top with the mozzarella cheese, leaving a 1/2-inch border. Carefully slide the pizza onto the preheated pizza stone, cover the grill and bake until the crust is golden brown, 10 to 12 minutes.
- Using a pizza peel, transfer the pizza to a cutting board and cut into slices. In a bowl, toss together the arugula, olive oil, vinegar, salt and pepper and scatter evenly over the pizza. Cut each slice of prosciutto in half lengthwise and drape over the arugula. Top with the Parmigiano-Reggiano cheese and serve immediately. Serves 2.