Preheat the oven to 375 degrees. Chop and toast your walnuts, until fragrant. Butter the inside of a 9 x 13-inch baking pan. In a bowl, mix together the oats, walnuts, baking powder and cinnamon. In another bowl, whisk together the maple syrup, milk, eggs, and vanilla. Add the melted butter and whisk to combine. Arrange the bananas & strawberries in a single layer at the bottom of the baking dish. Cover the fruit with the oat mixture. Slowly pour the milk mixture over the oats. Layer the remaining fruit on the top and sprinkle with cinnamon. Bake for 35-40 minutes, until the top is golden and the oat mixture has set. Let cool slightly before serving. Drizzle with maple syrup and enjoy!