Grease a 20-cm pan with butter and dust with little flour. Preheat oven 175°C (350°F).
Combine the flour, baking powder and salt.
Beat the eggs, sugar and orange zest on high speed in a bowl until smooth. Add the oil and continue beating until the batter doubles in size. Lower speed and gradually add the flour mixture and the orange juice. Continue beating until batter is creamy.
Pour the batter into the prepared pan and bake for about 50 Do the toothpick test. Let cool on a wired rack.
For the glazing: Heat all the ingredients in a heavy saucepan over low heat, stirring constantly until smooth. Spread on cake while still warm.