Preheat the oven to 350°F and grease an 8×8-inch or similar baking dish.
In a large bowl, whisk together the mashed banana, milk, almond butter, maple syrup, and melted nutterl. Add the baking powder, cinnamon, and salt and whisk again.
Fold in the oats, ¾ cup of the nuts, and ½ cup of the blueberries. Pour the mixture into the prepared baking dish and smooth into an even layer.
Top with the remaining ½ cup blueberries, the remaining ¼ cup nuts, the brown sugar, and coconut flakes.
Bake for 40 to 50 minutes, or until the topping is crisp and the middle is set. Remove from the oven and let cool for 10 minutes before serving.