Preheat the oven to 425 degrees F (220 degrees C). Grease a 12-cup muffin tin or line cups with paper liners.
Whisk milk, oil, and egg together in a bowl until evenly blended. Stir oats, flour, sugar, baking powder, and salt together in a separate bowl, making a well in the center. Pour milk mixture into well and stir just until batter is combined; fold in blueberries.
Spoon batter into the prepared muffin cups, filling each ⅔ full.
Bake in the preheated oven until tops spring back when lightly pressed, about 20 to 25 minutes. Cool in the tin for 5 minutes. Transfer to a wire rack to cool completely.
