1. Preheat oven to 450° and butter a 9- by 13-in. baking dish. In a large bowl, toss potato slices with lemon juice, olive oil, oregano, lemon zest, garlic, and salt; layer slices in baking dish.
2. Pour 1 cup boiling water over potatoes and bake, uncovered, until most of the water has evaporated and potatoes are tender, about 30 minutes. Top with feta and bake until golden, about 15 minutes more.
Note: Nutritional analysis is per serving.