1. Preheat oven to 475ºF. Brush bottom of a 16-by-11-inch rimmed baking sheet with 1 Tbsp. olive oil. Press and stretch dough evenly to cover bottom of sheet. (If dough resists at first, let it rest for a minute before continuing.) Toss potatoes with 1 Tbsp. oil and scatter over dough. Sprinkle with salt. Scatter spinach over potatoes. Sprinkle with cheese.
2. Bake until underside of crust is golden (lift an edge of pizza with a spatula to peek) and cheese is bubbling, about 20 minutes. Let stand 5 minutes on a wire rack before slicing.