Preheat oven to 350°F (175°C). Line a muffin tin with cupcake liners or lightly grease the cups.
In a medium bowl, mix whole wheat flour, oat flour, baking powder, and cinnamon.
In a second bowl, whisk together egg, applesauce, yogurt, and melted coconut oil until smooth.
Pour wet mixture into dry ingredients and stir until a thick batter forms. Do not overmix. Fold in blueberries gently.
Scoop batter into muffin cups, filling each about two-thirds full.
Bake for 18–22 minutes, until tops are set and a toothpick inserted in center comes out clean.
Cool in pan for 10 minutes, then transfer to a wire rack and cool completely before frosting.
For frosting: mix Greek yogurt, peanut butter, and mashed blueberries until smooth. Refrigerate for 15 minutes if too loose.
Spread a small spoonful of frosting on each cooled cupcake. Optionally top with a blueberry.
Serve one cupcake as a treat. Store leftovers in refrigerator for 3–4 days or freeze for longer storage.