Preheat oven to 450°. Roll pizza crust dough into a 12-inch circle. Transfer to a baking sheet sprinkled with cornmeal. Spread mashed sweet potatoes over dough. Top with turkey, spinach, sliced shiitake mushrooms, sliced red onion, shredded Havarti cheese, and freshly ground Italian seasoning. Bake directly on oven rack 18 minutes or until edges are browned.