Preheat oven to 425°; spray rimmed baking pan with cooking spray. In large bowl, whisk eggs; stir in potatoes, ½ cup Cheddar cheese, Parmesan cheese, ¼ cup green onions, salt and pepper. On prepared pan, shape potato mixture into 11 ½-inch circle; bake 23 minutes or until bottom and edges are golden brown.
Top crust with chicken and remaining ½ cup Cheddar cheese; bake 7 minutes or until cheese is melted and crust is crisp.
Drizzle pizza with dressing; top with remaining 2 Tbsp green onions and hot sauce, if desired. Cut pizza into 8 slices.