Preheat your oven to 350°F (175°C), and prepare a 9x5 inch loaf pan by greasing it and dusting with flour.

In a large bowl, whisk together the dry ingredients: all-purpose flour, baking soda, salt, ground cinnamon, and optional nutmeg.

In a medium bowl, combine granulated sugar, vegetable oil, eggs, and vanilla extract and whisk until smooth.

Fold the wet mixture into the dry ingredients until just combined. Then gently fold in the grated zucchini.

In a small bowl, mix flour, brown sugar, and ground cinnamon for the streusel. Cut in cold butter until it resembles coarse crumbs.

Pour the batter into the prepared loaf pan, sprinkle with streusel, and bake for 50-60 minutes or until a toothpick comes out clean.

Let the bread cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.