Preheat your oven to 375°F. Grease a 9x5x3" loaf pan with cooking spray and set it aside.

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

Cream together softened butter and sugar until fluffy.

Add eggs one at a time, mixing well after each addition.

Mix in vanilla extract and orange zest.

Alternate adding flour mixture and sour cream to the butter mixture, starting and ending with the flour.

Gently fold in the diced rhubarb.

Pour the batter into the prepared loaf pan, smoothing the top, and bake for about 60 minutes, or until a cake tester comes out clean.

Let the bread cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.

Store leftovers in an airtight container for up to a few days.

Sift powdered sugar into a bowl.

Combine sifted powdered sugar with fresh orange juice until a thick icing forms.

If the icing is too thin, add more powdered sugar. If it's too thick, add orange juice a few drops at a time until desired consistency is reached.

The icing should be thick enough to form a nice layer on the cake.