Preheat the oven to 350°F. Line a 9x5-inch baking pan with parchment paper.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and cinnamon.
Add the apple juice and vanilla extract, stirring until fully incorporated (batter will be thick).
Stir in the zucchini and walnuts, then transfer to the prepared baking pan.
Bake, uncovered, for 50 minutes, or until a toothpick inserted into the center comes out clean.
Cool in the pan for 10 minutes, then lift the bread out of the pan and set on a cooling rack to cool completely. Slice and serve at from temperature.