Preheat oven to 340F (170C). Line a bottom of 8-inch (20cm) round pan with parchment paper and grease the bottom and sides.
Place peeled pistachio in a powerful blender and blend into flour. Set aside. Note: you can use store-bought ground pistachios.
In a large bowl beat egg yolks with sugar on high speed, until thick, smooth and pale. Add oil, vanilla extract and lemon zest. Beat until incorporated.
Add ground pistachios and fold until incorporated. Set aside.
In a separate bowl beat egg whites with pinch of salt. Beat until foamy, then gradually add 2 tablespoons of sugar and beat until stiff peaks form.
Gradually fold the egg whites into egg yolk mixture, 1-2 tablespoons at the time. Fold just until combined after each addition, do not over fold.
Pour the batter to the prepared pan, sprinkle some chopped pistachios on top.
Bake for 30 minutes or until golden brown on top. Let cool in the pan for 10 minutes, release from the pan and let cool completely.