Preheat the oven to 350°F and grease two oven-safe, 6 to 8-ounce ramekins with butter or cooking spray. (See notes for microwave instructions.)
In a blender, add rolled oats, milk, banana, egg, maple syrup, baking powder, salt, and vanilla extract, and blend or puree until a smooth batter is formed. (If your blender is not very strong, add the rolled oats on their own and blitz them into an oat flour, and then add the remaining ingredients and blend until a smooth batter forms.)
Pour the mixture into the ramekins and then sprinkle blueberries, dividing them evenly across the two ramekins.
Transfer ramekins to the oven and bake for 25-30 minutes until they have risen and are slightly golden around the edges.
Once baked, remove them from the oven, allow them to cool slightly, and then serve as it or with toppings of your choice.
Any leftovers can be stored, covered with a lid or plastic wrap, in the fridge for up to 4 days or in the freezer for 3 months.
To Make Blended Baked Oats in the Microwave: Follow steps 1-3 as outlined, then place ramekins in the microwave and cook on high for 3-5 minutes until oats have risen and are fully cooked.