Preheat oven to 350 degrees. Grease and flour the tin.
Sift together the flour, salt, spices, baking soda and baking powder into a large bowl.
Using the pastry blender (or your hands - but working quickly), rub the butter into the flour mixture. It should resemble breadcrumbs.
Add the eggs and stir to combine.
Add the sugars and mix well. Now here's where you have to trust me on this one. At this point, the mixture will look a little clumpy and you may wonder how this will form a light and lovely crumb. Trust the process!
Add the gratered zucchini. Mix well. The moisture from the zucchini will soak into the thick batter and relax everything together to give a smooth consistency to the batter.
Spread the batter in an even layer in the greased and floured tin.
Prepare the crumble by mixing the brown sugar, flour, cinnamon and melted butter in a small bowl. Break up the mixture into small pieces.
Sprinkle the crumble mixture evenly over the top of the cake.
Bake in preheated oven for 40 minutes or until a toothpick inserted in the center comes out clean.
Allow to cool completely. Slice and enjoy!