1. Preheat your oven to 350°F (175°C) and grease a 9×5-inch loaf pan. Optionally line with parchment paper for easier removal.

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

3. In a separate large bowl, whisk the eggs, granulated sugar, brown sugar, oil, and vanilla extract until well combined.

4. Fold in the shredded zucchini and chopped apple until evenly incorporated.

5. Gradually add the dry mixture to the wet mixture and stir just until combined. Do not overmix.

6. Pour the batter into the prepared loaf pan, smoothing the top.

7. Bake for 50–60 minutes, or until a toothpick inserted into the center comes out clean. Cool in the pan for 10 minutes, then transfer to a wire rack.

8. While the bread cools, make the frosting: In a small saucepan, melt butter and brown sugar over medium heat for 2–3 minutes, stirring continuously.

9. Add milk and vanilla, then remove from heat. Let cool slightly and whisk in powdered sugar until thick and spreadable.

10. Once the loaf is completely cooled, spread the frosting generously on top and let it set before slicing.