Preheat the oven to 350 degrees F. Line a 9" round baking pan (or spring form pan) with parchment paper and set aside.
In a medium bowl, whisk together your dry ingredients.
In a separate bowl, combine your eggs, oil, vanilla and 1/2 cup coconut milk. Beat these into the dry ingredients until a very thick batter begins to form. Slowly add the rest of your coconut milk, one tablespoon at a time. You want the dough to be slightly thicker than a cake batter. Fold in the lemon zest and blueberries.
Transfer the mixture into your baking pan and set aside.
Prepare the crumb topping by combining all the ingredients into a small bowl and beat until you have a sandy texture. Sprinkle the mixture evenly over the top of the cake.
Bake in the center of your warmed oven for 40 - 45 minutes. Test with a cake tester by placing it in the center of the cake. If there is nothing on the stick when you remove it, the cake is ready!
Remove from oven and allow to cool for 10 - 15 minutes before transferring to a wire rack to cool completely.