Preheat the oven to 350F. Butter an 8x4-inch loaf pan or spray with baking spray with flour.

In a large bowl, whisk together flour, baking powder, and salt.

In another large bowl, combine sugar and orange zest. Rub the zest into the sugar with your fingers until the sugar is a light orange color. Add the oil, eggs, orange juice, and vanilla, and whisk until combined. Pour into the flour mixture and whisk together just until all of the flour is incorporated. Pour the batter into the prepared cake pan.

Bake for 1 hour and 10 minutes or until a wooden toothpick inserted into the center comes out with a few moist crumbs, covering loosely with foil after about an hour if it's looking very brown on top. Let the cake cool in the pan for 15 minutes. Remove and cool completely on a wire rack.

In a small bowl, whisk together confectioners' sugar, zest, and juice until smooth. Drizzle over the cooled cake and let it stand for 30 minutes to set. Store the cake in an airtight container for up to 5 days.