In a bowl, sift flour and baking powder. Set aside.
In another bowl, add in sugar and eggs. Whisk until the mixture is pale in color. Add in lemon zest, sunflower oil, vanilla extract and mix until well combined. Then add in plain yogurt and mix to combine.
Add in previously sifted flour mixture and mix just until everything to combine. Do not overmix to avoid hard, dense cake. Pour cake batter into a 9 inch (23x23 cm) square pan that has previously been greased and floured. Spread the batter evenly.
Bake at 180ºC (350ºF) preheated oven for 35-40 minutes or until the cake is golden brown and fully cooked. Remove from the oven and leave for 5 minutes before taking it out from the pan. Leave to cool completely on a rack before slicing. Dust with icing sugar if you want, slice and enjoy!
For this recipe I'm using a yogurt container of 150 gr (5.3 oz).