Preheat oven to 375. Grease a 1-1/2 quart casserole dish.
Lay the bananas in a single layer in the bottom of the dish. Sprinkle 1/2c of the blueberries over bananas.
In a bowl, combine the oats, cinnamon, baking powder, and salt. Stir and sprinkle over fruit.
Whisk milk, egg, butter, syrup, and vanilla. Pour over oats, coating evenly. Sprinkle remaining blueberries and walnuts over top. Bake for 35-45 minutes or until golden and bubbly and set in the center.
Serve with milk.