Peel plantains and slice diagonally 1/4 inch thick. Pour oil into a 12- by 15-inch baking pan; add plantains and 1/2 teaspoon salt and mix to coat. Transfer half the plantains to a second 12- by 15-inch baking pan and spread slices in both pans into a single layer.
Bake in a 400° regular or convection oven, turning plantains occasionally with a wide spatula, until browned on the outside and tender when pierced, 15 to 20 minutes; switch pan positions halfway through baking. Serve plantains warm. Add more salt to taste.