Heat the frozen blueberries, sugar and water in a small pot over a medium heat. Once the mixture starts to bubble, turn the heat down to low and let simmer and soften for 10 minutes. Take off the heat and mash slightly with the back of a fork.
In a medium bowl, mix the oats, milk, cooked blueberries and dried blueberries until combined.
Divide between two bowls or mason jars and store in the fridge overnight.
In the morning, top with the fresh blueberries and serve.