Preheat the Oven: Preheat your oven to 350°F (175°C) and grease a mini muffin tin.
Combine Dry Ingredients: In a large bowl, mix the all-purpose flour, whole wheat flour, oats, sugar, baking powder, and salt.
Mix Wet Ingredients Separately: In another bowl, whisk together the milk, Greek yogurt, melted butter, egg, and vanilla extract until well combined.
Blend Wet and Dry Mixtures: Gradually add the wet ingredients to the dry ingredients, stirring gently until combined. Be careful not to overmix.
Add Blueberries: Gently fold in the blueberries, not crushing them.
Fill Muffin Tin: Spoon the batter into the prepared muffin tin, filling each cup about three-quarters full.
Bake: Bake for 12-15 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Cool: Allow the muffins to cool in the tin for a few minutes before transferring them to a wire rack to cool completely.