Preheat oven to 375 degrees F. Line muffin pan with silicone muffin cups and spray with cooking spray.
Add ½ cup granulated sugar, ½ cup softened butter to medium mixing bowl. Beat with hand mixer until mixture is smooth and fluffy.
Add 1 ½ ripe bananas, 1 egg, ½ cup milk, and 1 teaspoon lemon juice to batter. Beat until smooth.
Add 1 cup all purpose flour, ½ cup whole wheat flour, 2 teaspoons baking powder, ½ teaspoon salt. Beat on low and until just barely incorporated.
If using frozen blueberries, sprinkle 2 teaspoons flour over 1 ½ cup blueberries, and mix until blueberries are coated. This will prevent some bleeding from the blueberries and keep them from all sinking in the mixture.
Add blueberries and ¾ cup oats to mixture. Carefully fold them into batter with rubber spatula.
Using a large spoon or cookie scoop, divide batter evenly between 12 muffin cups. Sprinkle turbinado sugar over each muffin (about 2-3 Tablespoons worth).
Bake for 15-18 minutes, or until a toothpick comes out clean.
Store in airtight container for a couple days, or in freezer bag for months.