Preheat your oven to 350°F (175°C) and grease and flour a 9×5 inch loaf pan.

In a large mixing bowl, combine 2 cups of all-purpose flour, 1 teaspoon of ground cinnamon, 1 teaspoon of baking soda, 1 teaspoon of salt, and ¼ teaspoon of ground nutmeg. Whisk together until well blended.

In another bowl, whisk together 1 cup of granulated sugar, ½ cup of vegetable oil, 2 large eggs, and 1 teaspoon of vanilla extract until smooth and slightly frothy.

Gently add the wet mixture to the dry ingredients, stirring until just combined.

Incorporate 1 ½ cups of grated zucchini into the batter, and fold in ½ cup of chopped walnuts or pecans if desired.

Pour the batter into your greased loaf pan and smooth the top with a spatula.

In a small bowl, mix together ¼ cup of all-purpose flour, ¼ cup of light brown sugar, ¼ cup of granulated sugar, and 1 teaspoon of ground cinnamon. Cut in ¼ cup of cold unsalted butter until it resembles coarse crumbs.

Sprinkle the streusel mixture over the batter in the loaf pan and bake for about 50–60 minutes, or until a skewer inserted in the center comes out clean.

Let the bread cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.