Preheat the oven to 350°F (175°C). Grease and line a round or rectangular cake pan with parchment paper.

1. In a medium bowl, whisk together flour, baking powder, salt, and cinnamon (if using). Set aside.
2. In a large bowl, beat eggs and sugar until light and fluffy.
3. Add olive oil, milk, vanilla extract, and citrus zest to the egg mixture. Mix until well combined.
4. Gradually add the dry ingredients to the wet mixture, stirring until a smooth batter forms.
5. Fold in half of the sliced apples into the batter.
6. Pour the batter into the prepared pan and arrange the remaining apple slices on top in a fan or rustic pattern.
7. Bake for 45–50 minutes, or until golden brown and a toothpick inserted into the center comes out clean.
8. Let the cake cool in the pan for 15 minutes before transferring to a wire rack to cool completely.
9. Dust with powdered sugar before serving, if desired.