Preheat the oven to 350°F (175°C) and grease an 8x8-inch baking dish or line it with parchment paper.

Mix the dry ingredients: In a large bowl, combine the rolled oats, whole wheat flour, baking powder, baking soda, and salt. Stir until well mixed.

Prepare the wet ingredients: In a separate medium bowl, whisk together the Greek yogurt, milk, eggs, vanilla extract, honey, and melted coconut oil until smooth.

Combine the wet and dry ingredients: Gradually add the wet ingredients to the dry mixture, stirring gently until just combined. Be careful not to overmix.

Fold in the blueberries: Gently fold in the blueberries, making sure they are evenly distributed throughout the batter.

Bake the cake: Pour the batter into the prepared baking dish and spread it out evenly. Place in the preheated oven and bake for 30 to 35 minutes, or until a toothpick inserted into the center reveals no batter.

Let it cool: After 10 minutes, remove the cake from the pan and set it on a wire rack to cool entirely. Cut into slices and savor as a healthy breakfast or snack!