Preheat the oven to 375 degrees and grease a 9-inch square baking pan (or similar).
In a small bowl, mix together the flour, baking powder, and salt. Set aside.
In a large bowl, mix together the egg, maple syrup, coconut oil, and vanilla. Slowly add the flour mixture, alternating with the coconut milk. Gently stir in the blueberries. Transfer the batter to the prepared pan.
To make the topping, mix together the oats, cornmeal, coconut, and cinnamon in a small bowl. Add in the coconut oil and maple syrup, then mix to combine. Distribute the topping evenly on the cake batter.
Bake for about 40 minutes, or until the topping is golden and a toothpick inserted in the center of the cake comes out clean.