1. Preheat oven to 350°F (175°C). Grease a 9×5-inch loaf pan or line with parchment paper.

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

3. In another bowl, whisk eggs, brown sugar, vegetable oil, and vanilla until smooth.

4. Fold in grated zucchini and apple. Pat dry zucchini if watery.

5. Add dry ingredients to wet mixture and stir until just combined. Fold in nuts if using.

6. Pour batter into prepared pan. Bake 50–60 minutes or until a toothpick comes out clean.

7. For frosting, melt butter and brown sugar in a saucepan. Add milk and bring to boil. Remove from heat and whisk in powdered sugar until smooth.

8. Let bread cool for 10 minutes in pan, then transfer to wire rack. Once cool, drizzle with brown sugar frosting.