Preheat oven to 375°
Arrange the banana slices in a single layer on the bottom of a ceramic dish. Sprinkle the apples and half of the berries over the bananas, 1/3 tsp of the cinnamon, 1 Tbsp of the honey and cover with foil.
Bake 15 minutes, until bananas get soft.
Meanwhile, in a medium bowl, combine the oats, half of the nuts, baking powder, remaining cinnamon, and salt. Stir.
In a separate bowl, whisk together the remaining honey, milk, egg, and vanilla.
Remove the bananas from the oven. Pour the oat mixture over the bananas & berries.
Pour the milk mixture over the oats, making sure to distribute the mixture as evenly as possible over the oats. Sprinkle the remaining berries and walnuts over the top.
Bake the oatmeal for about 30 minutes, until the top is golden brown and oatmeal has set. Serve warm from the oven.