In medium bowl combine and mix walnuts, oats, salt, cinnamon, baking powder, and raisins. In separate small bowl whisk together milk, egg, butter, vanilla extract, and maple syrup. Cut and slice all bananas and lay at bottom of your casserole dish (mine was 8x10). Then take your dry mixture and evenly lay it over the bananas. Then drizzle your milk mixture over the top. Make sure to evenly coat and try to get the entire surface area covered. Bake for 35 minutes until it is golden brown along the edges. Serve.
