Preheat oven to 350 F. Melt chocolate, oil, and sugar in a sauce pan on med-low heat, stirring well so the ingredients are properly combined. Transfer to mixing bowl and allow to cool slightly. Sift gluten-free flour, cocoa and baking powder into the mixture and stir well. Add the beaten eggs. Stir until well blended.
Line an oiled 10 x 7 inch or 9 x 9 inch cake pan with parchment paper. Lightly oil paper. Pour in mixture. Let batter sit 30 min. Bake in preheated oven for about 35 minutes. Test with a toothpick in the centre to check that it's cooked through. Allow to cool completely.