Preheat the oven to 350°F. Line a 9-inch round baking pan with parchment paper and set aside.
In a medium bowl or stand-up mixer, combine your dry ingredients and whisk them together to combine.
In a separate bowl, combine your eggs, coconut oil, vanilla and half of the coconut milk. Beat these into the dry ingredients until a very thick batter begins to form. Slowly add the rest of the coconut milk, one tablespoon at a time until you have a smooth batter. You want the dough to still be slightly thick, thicker than a cake batter. Fold in the lemon zest and blueberries.
Scoop the mixture into your baking pan and smooth it over with the back of a wet spoon. Set the baking pan aside and prepare the streusel topping.
Streusel Topping
Combine all the ingredients into a small bowl and mix them together with a fork until you have a sandy, crumbly texture. Sprinkle the mixture evenly over the top of the cake.
Bake in the center of your warmed oven for 40 - 45 minutes until a cake tester comes out clean when inserted into the center of the cake.
Let the cake cool on a wire rack for 10 minutes and slice into 8 equal pieces. Serve slightly warmed with a steaming cup of coffee or tea.