01 - Preheat oven to 325°F. Line bottom of 8-inch round cake pan with parchment paper; do not grease sides.
02 - In medium bowl, whisk together flour, sugar, baking powder, and salt until well blended.
03 - In large bowl, whisk egg yolks, Greek yogurt, vegetable oil, vanilla extract, and lemon zest until smooth.
04 - Add dry ingredients to wet mixture and stir just until combined; do not overmix.
05 - Using electric mixer, beat egg whites in clean bowl until stiff peaks form.
06 - Gently fold one-third of beaten egg whites into batter to lighten. Fold in remaining whites carefully, retaining maximum air volume.
07 - Pour batter into prepared cake pan and smooth top surface evenly.
08 - Bake for 35-40 minutes until golden brown and toothpick inserted in center comes out clean.
09 - Cool in pan for 10 minutes. Run knife around edges, invert onto wire rack, and cool completely.
10 - Dust with powdered sugar before serving, if desired.