Preheat your oven to 350°F (175°C) and grease a 9x5 inch loaf pan with butter or cooking spray, then dust lightly with flour.

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

In a separate medium bowl, mix the granulated sugar and vegetable oil. Add in the eggs and vanilla extract, whisk until smooth.

Gently fold the wet mixture into the dry ingredients, then add the grated zucchini and fold in the nuts if using.

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

Pour the batter into the prepared loaf pan, spread evenly, and sprinkle the streusel topping generously over the batter.

Bake for 50-60 minutes or until a skewer comes out clean. If browning too quickly, tent with foil.

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