Preheat oven to 350F. Beat oil, sugar and eggs in a bowl with a wire whisk until light. Combine flour with baking powder, ground almonds and orange zest. Add to oil and sugar mixture stirring in gently. Spread mixture in a greased rectangular pan 22 x11 cm 8.65 x 4.35 inches and bake for 50 minutes. Lower heat to 330F and continue baking for 10 minutes more. Test cake in the center for dryness. If still moist, allow to bake a little longer. Cool cake, remove from pan and dust with powdered sugar.