Place 2 phyllo pastry sheets at the bottom of a greased tray, sprinkle them with oil and walnuts. Arrange all the phyllo pastry sheets this way.
The topmost sheet needs to not have any walnuts - only a little oil. Cut it into diamonds or squares.
Bake at 320°F (160 °C) until golden. Boil a syrup from the water, sugar and lemon juice.
Pour the hot syrup over the cooled baklava.