In large bowl, sift flour, granulated sugar, baking powder and salt. Add oil, egg yolks, lemon juice, water and lemon zest; whisk until well combined. In large bowl, beat egg whites and cream of tartar with electric mixer to stiff peaks. Fold 1/3 of whipped whites into the batter to lighten. Gently fold in the remaining whites until mixture is combined; do not overmix or batter will deflate. Pour into ungreased pan; tap gently on counter to release air pockets.