Preheat the oven to 325°F (162°C) and coat two 8 x 4-inch (20 cm x 10 cm) pans with nonstick spray.
In a stand mixer, beat the eggs, oil, sugar, and vanilla extract on medium speed using the paddle attachment.
Add the salt, baking soda, baking powder, cinnamon, and nutmeg, and mix until thoroughly incorporated. Then, mix in the flour in thirds, scraping down the bowl as needed to ensure the ingredients are well combined.
Stir in the zucchini and walnuts until well combined.
Divide the batter evenly between the two pans and bake for 1 hour, or until a toothpick inserted into the center comes out clean.
After placing the bread in the oven, prepare the crumb topping by combining all the ingredients in a bowl and mixing with your hands until large crumbles form. Once the bread has baked for 15 minutes, divide the crumbs evenly and scatter them over the top of each pan of bread. Continue baking.
Allow the bread to rest on the counter for 20 minutes before removing it from the pan and cooling completely on a wire rack.
Notes
For more green coloring in the bread, grate the zucchini on a larger-sized setting.