Make the cake: Whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, whisk together the sugar, eggs, yogurt, and vanilla until creamy. While whisking, slowly add in the coconut oil until combined. Add the dry ingredients to the wet ingredients and whisk together — the batter will be thick. Do not overmix. Spread batter into the prepared pan. Set aside.
Make the crumb topping: Using a fork, mix the flour, brown sugar, and cinnamon together in a small bowl. Stir in the coconut oil until crumbs form.
Sprinkle the blueberries all over the top of the batter. Sprinkle the crumb topping, and the chopped walnuts on top.
Bake for 38-42 minutes. Baking times can vary, so keep an eye on it. The cake is done when a toothpick inserted in the center comes out clean, or with moist crumbs. Remove the cake from the oven and allow to cool on a wire rack. After the cake cools for a few minutes, slice and serve. It's served best with a dusting of confectioners' sugar.
The cake is best served within a few days. However, it can be stored in the refrigerator for up to 5 days when covered tightly.
1Because this cake rises a decent amount, it's best to use a springform pan.2If the top of the cake is browning too quickly, loosely cover it with aluminum foil.