Preheat oven to 350 degrees F. Prepare a loaf tin by lightly coating with cooking spray and lining with parchment paper.
In a large bowl, combine oil, brown sugar and white sugar. Add eggs and vanilla and combine until thoroughly mixed. Add zucchini and stir until distributed.
In a smaller bowl, sift together flour, salt, baking powder, baking soda and cinnamon. Add flour mixture to zucchini mixture and stir until all of the flour in incorporated. Wash the blueberries and place them in a small bowl with 2 Tbs of gluten free flour and toss to coat the blueberries well. Gently fold the blueberries into the zucchini mixture, stirring only enough to mix the blueberries throughout.
Pour mixture into prepared tin and bake for 10 minutes. Meanwhile, combine topping ingredients in a small bowl until crumbly. After the loaf has baked for 10 minutes, remove from oven and sprinkle the topping evenly over the top. Place back in oven and bake for another 60 minutes, for a total of 1 hour and 10 minutes of baking time.
Remove from oven and allow to cool slightly before removing the loaf from the pan to finish cooling.