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 until light orange. Add the oil, eggs, orange juice, and vanilla, and whisk until combined. Pour into the flour mixture and whisk together until all flour is incorporated.

Pour the batter into the prepared cake pan.

Bake for 1 hour and 10 minutes or until a toothpick comes out with a few moist crumbs. Cover loosely with foil after an hour if it's very brown on top. Let it cool in the pan for 15 minutes, then 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 set for 30 minutes.

Store the cake in an airtight container for up to 5 days.