Preheat oven to 400 degrees. Lightly coat a 9-by-13-inch baking pan with oil; set aside. Bring a large saucepan of heavily salted water to a boil. Add sliced potatoes, and blanch until nearly tender. Meanwhile, place 1 tablespoon oil in a medium bowl. Drain potatoes thoroughly, and add to bowl with oil; mix to coat. Spread potatoes in the prepared baking pan.
Arrange fish fillets over potatoes without allowing fillets to touch each other. Spoon salsa over the fillets and potatoes. Bake until fish is just done, 10 to 15 minutes. Sprinkle with cilantro, and serve immediately.