Make topping first by mixing flour, sugar and cinnamon. Then add chilled butter (in small chunks). Use a pastry cutter to crumble the butter into the dry mixture, or just use your hands, until mixture is crumbly. Refrigerate.
Blend coconut sugar, oil and butter, then add egg, vanilla extract and lemon zest. Combine flour, baking powder and salt in separate bowl, then add to liquid mixture, alternating with the milk. Finally, add blueberries, batter will be thick and almost like dough.
Line a greased 8-inch square pan with parchment paper and pour batter into pan. Remove topping from. Refrigerator and evenly spread on top of the batter. Bake at 350 degrees for 40-45 minutes, until inserted toothpick comes out clean. Cool for an hour, if you can wait.
Enjoy!