Preheat the oven to 375 degrees. Butter an 8" square baking dish.
In a large bowl, combine the oats, sugar, baking powder, cinnamon and salt.
In a small bowl whisk together the milk, egg & butter.
Slice the bananas into the bottom of the baking dish. Cover the bananas with 1/3 of the berries. Spoon in the oat mixture, and then pour the milk mixture on top evenly. Press the remaining berries into the oats, and sprinkle with cinnamon.
Bake for 35-45 minutes, until the mixture of bubbling vigorously and the edges are lightly browned. Serve immediately.