01 - Preheat oven to 325°F. Line bottom of 8-inch round cake pan with parchment paper, leaving sides ungreased.
02 - Whisk flour, sugar, baking powder, and salt in medium bowl until evenly blended.
03 - Whisk egg yolks, Greek yogurt, vegetable oil, vanilla, and lemon zest in large bowl until smooth.
04 - Add dry ingredients to wet mixture and stir just until combined.
05 - Beat egg whites with electric mixer in clean bowl until stiff peaks form.
06 - Gently fold one-third of beaten egg whites into batter to lighten. Fold in remaining egg whites carefully to maintain air volume.
07 - Pour batter into prepared pan and smooth top evenly.
08 - Bake 35–40 minutes until golden brown and toothpick inserted into center comes out clean.
09 - Cool in pan 10 minutes. Run knife around edges, invert onto wire rack, and cool completely.
10 - Dust with powdered sugar before serving, if desired.