Preheat the oven to 180°C (350°F).
In a large bowl, combine the flour, sugar, baking powder, baking soda, cinnamon, nutmeg, and salt. Mix well.
In another bowl, whisk together the olive oil and orange juice. Add the orange zest and mix to combine.
Gradually add the wet ingredients to the dry ingredients, stirring until just combined.
Fold in the chopped walnuts and raisins if using.
Pour the batter into a greased 30cm (12-inch) round cake pan.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove from the oven and let cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
Dust with powdered sugar before serving. Enjoy your Fanouropita!