Grease two 8 x 4-inch loaf pans with vegetable oil and preheat the oven to 325°F (163°C).

Grate the zucchini and chop the apple into small pieces. Set aside.

In a large bowl, combine all-purpose flour, ground cinnamon, salt, baking powder, and baking soda. Whisk until well blended.

In another bowl, whisk together eggs, vegetable oil, vanilla extract, white sugar, and brown sugar until smooth.

Gradually pour the wet mixture into the dry ingredients and fold gently until just combined.

Fold in grated zucchini, diced apple, and chopped walnuts and let the mixture rest for 5 minutes.

Pour the batter into the prepared loaf pans and bake for 55 minutes or until a toothpick comes out clean.

Let the bread cool in the pans for 20 minutes before transferring to a wire rack to cool completely.