Preheat oven to 180C/350F. Line and grease a 9x5" loaf tin.
Sift flour and baking powder into a bowl. Add the sugar and and mix with a wooden spoon.
In a separate bowl mix together the oil, milk, orange juice, orange zest and vanilla.
Pour the wet ingredients into the dry ingredients and mix until just combined.
Pour into the loaf tin and place in the oven for 45-55 minutes. It should be starting to turn golden brown on the edges. Do the toothpick test and once it comes out clean, its ready. If it's not, leave in for a few more minutes.
Make the icing by mixing the icing sugar and orange juice together until it forms a thick icing. Spoon onto the cake once cooled with the back of a spoon.
Top with some extra orange zest and serve! Will make about 8-10 slices.
Will keep in an air tight container for 3-4 days.