Whisk the minced garlic into the olive oil and spread over crusts. Sprinkle mozzarella and Grana Padano cheeses over and broil on top rack of the oven until bubbly, about 5 minutes (watching closely).
Divide Prosciutto di Parma between pizzas. Top each pizza with a handful of arugula. Drizzle the greens with olive oil and a squeeze of lemon, then finish with a few more shavings of Grana Padano.