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 uniformly blended.
03 - Whisk egg yolks, Greek yogurt, oil, vanilla, and lemon zest in large bowl until smooth and creamy.
04 - Add dry ingredients to wet mixture, stirring just until flour disappears. Avoid overmixing.
05 - Beat egg whites in clean bowl with electric mixer until stiff glossy peaks form.
06 - Gently fold one-third of beaten whites into batter to lighten. Fold in remaining whites carefully, preserving air pockets.
07 - Pour batter into prepared pan, smoothing top. Bake 35–40 minutes until golden and toothpick inserted center comes out clean.
08 - Cool in pan 10 minutes. Run knife around edges, invert onto wire rack. Cool completely before dusting with powdered sugar.