Preheat the oven to 400 degrees F. Using a pastry brush, lightly grease 2 large baking sheets with 1 teaspoon of oil each and set aside.
Using a mandoline slicer, or heavy, sharp knife, cut the sweet potatoes as thinly as possible. On 1 baking sheet, arrange the cut potatoes in 1 layer. On the second sheet, arrange the cut sweet potatoes in 1 layer. With a pastry brush, lightly coat the top side of both potatoes with the olive oil. Bake until golden and crisp, rotating the pans halfway through the cooking time, about 10 minutes. Remove from the oven.
While the potatoes are cooking, In a small bowl, combine the salt, rosemary, lemon zest, and black pepper.
Remove the potatoes from the oven and transfer to paper towels. While still warm, sprinkle the potatoes with the lemon salt mixture