Preheat the oven to 350°F. Grease three 4-inch springform or cake pans with coconut oil.
In a large bowl, combine the oat flour, oats, baking powder, and baking soda.
In a separate bowl, combine the water, egg, applesauce, and coconut oil until well-blended.
Add the wet ingredients to the dry ingredients and stir to combine.
Add 1/2 cup blueberries and gently stir them into the batter.
Divide the batter evenly between the prepared pans.
Bake for 22-25 minutes, or until a toothpick inserted in the center comes out mostly clean. Allow the cake layers to cool completely in the pans then remove them from the pan.
Spread ¼ cup of Greek yogurt on top of each layer. Stack the layers. Sprinkle the remaining ¼ cup of blueberries on top.
Store leftovers in an airtight container in the fridge.