Preheat oven to 350°F (177°C). Grease an 8-inch or 9-inch square or round baking pan, springform pan, or pie dish or line with parchment paper. Set aside.

With a fork, mix the flour, brown sugar, and cinnamon together in a small bowl. Mix in the melted butter. Don’t over-mix; you want the flour-y crumbles. Place in the refrigerator while you make the cake batter.

Whisk the flour, baking powder, baking soda, salt, cinnamon, and nutmeg together in a large bowl. Whisk the butter, brown sugar, granulated sugar, egg, and vanilla extract together in a medium bowl, then whisk in the shredded zucchini. Pour the wet ingredients into the dry ingredients and mix until combined. Batter will be thick. Pour/spread into prepared baking pan, then sprinkle the crumb topping evenly on top.

Bake for 35-38 minutes or until a toothpick inserted in the center of the cake comes out mostly clean with no wet batter. (A few moist crumbs are ok!) If you find the top of the cake is browning too quickly in the oven, loosely cover it with aluminum foil.

Remove the cake from the oven and set on a wire rack. Allow to slightly cool for a few minutes before slicing. I suggest drizzling with vanilla icing while the cake is still warm!

Cover leftover cake tightly and store in the refrigerator for up to 5 days.