Preheat the oven to 350°F and lightly grease a 6-inch round cake pan or line it with parchment paper.

Add the rolled oats to a blender or food processor and blend until they form a fine oat flour, then transfer to a small bowl and set aside.

In a medium mixing bowl, mash the ripe banana with a fork until mostly smooth.

Whisk the egg into the mashed banana until well combined.

Add the unsweetened applesauce and peanut butter to the bowl and whisk or stir until the mixture is smooth and creamy.

Add the oat flour to the wet mixture and stir with a spatula or spoon until no dry flour remains and a thick batter forms.

Gently fold in the fresh blueberries, distributing them evenly without crushing them too much.

Spoon the batter into the prepared cake pan and smooth the top with a spatula.

Bake for 20 to 25 minutes, or until the cake is set in the center and a toothpick inserted in the middle comes out clean.

Remove the cake from the oven and let it cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.

Once fully cooled, optionally top with a thin layer of dog-safe yogurt and extra blueberries, then slice and serve to your dog in appropriate portions.