Preheat the oven to 340F (170C). Line the bottom and the sides of an 8” (20cm) springform pan with parchment paper.
In a bowl, combine the flour, baking powder, and salt. Set aside.
In another bowl, add the egg, vanilla extract, and sugar. Whisk until pale yellow and well combined.
Add the oil, milk, orange juice, and orange zest and mix to combine.
Add the dry ingredients and mix just until no dry ingredients remain, and the batter has a homogeneous consistency.
Pour the batter into the prepared pan and bake for 45 minutes or until a toothpick inserted into the middle of the cake comes out clean.
Allow the cake to cool in the pan for 10 minutes before removing it to cool further.
Melt the chocolate and add the oil. Mix well to combine.
Pour the chocolate on top of the completely cooled cake. Refrigerate for 30 minutes and serve.