Preheat the oven to 350 degrees and grease an 8×4-inch loaf pan with baking spray.
In a large bowl, whisk together flour, baking soda, and salt.
In a separate bowl, combine sugar and orange zest, rubbing the zest into the sugar with your fingertips until well combined. Add the oil, melted butter, eggs, orange juice, and vanilla, and whisk until smooth.
Pour the wet ingredients into the flour mixture and whisk together until the flour is incorporated, but be careful not to overmix. Pour the batter into the prepared loaf pan.
Bake for 60-70 minutes or until a toothpick inserted into the center comes out mostly clean.
While the cake is baking, whisk together powdered sugar, zest, and juice in a small bowl until smooth. Set aside.
Let the cake cool in the pan for 15 minutes before removing from the pan to cool completely on a wire rack. Top with icing and garnish with orange slices. Enjoy! Store in an airtight container in the refrigerator for up to 5 days.
Notes
In order to make the recipe gluten free, simply sub out the flower for your favorite alternative!