Preheat oven to 400°F, with racks in center and lower positions.
Scrub sweet potatoes and then cut into ⅛ inch slices. A mandolin works great for thin slices Divide sweet potatoes between 2 rimmed baking sheets.
Drizzle with oil, toss, and sprinkle with salt and Parmesan, spread them in a single layer on sheets.
Bake, flipping once, until centers are soft and edges are crisp, 22 to 25 minutes.