Preheat your oven to 350°F (175°C). Grease a loaf pan.
In a bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
In another bowl, mix oil, brown sugar, granulated sugar, eggs, and vanilla extract until well combined.
Add the dry ingredients to the wet ingredients and mix until just combined. Fold in the grated zucchini.
Pour the batter into the prepared loaf pan.
For the streusel, mix brown sugar, flour, and cinnamon in a small bowl. Cut in the cold butter until the mixture resembles coarse crumbs. Sprinkle over the batter.
Bake for 60 minutes or until a toothpick inserted into the center comes out clean. Let it cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.