Preheat oven to 350oF (175oC).
Line baking pan with parchment paper.
In the small bowl sift all-purpose flour and baking power. Set aside.
In the mixing bowl whip eggs and granulated sugar until light and fluffy.
Add vegetable oil and warm milk. Mix well.
. Add flour mixture and orange zest. Mix with spatula.
Transfer batter into baking pan and level up with spatula.
Bake at 350oF (175oC) for 15-18 minutes or until clean toothpick.
Remove cake sponge from the oven and let cool completely. Cover it into plastic wrap and keep in the refrigerator.