Place dough ovals on oiled grates (if your grill is small, work in batches of 4); grill, covered, until grill marks appear, 3 to 4 minutes. Remove from grill, and place, grilled side up, on a baking sheet. Spread each crust with about 2 tablespoons arugula pesto. Top evenly with mozzarella and sliced summer squash. Return pizzas to grill grates, and grill, covered, until cheese is melted and crust is cooked through, 4 to 5 more minutes. Remove from grill.