Spray an 8X8in baking dish with cooking spray, set aside. Preheat oven to 375°F.
In a large mixing bowl, blend together oats, sugar, baking powder, cinnamon, salt, chopped walnuts, sliced strawberries, and chocolate chips (optional). Pour into prepared baking dish.
Melt butter and cool slightly. In a small bowl, whisk together the milk, egg, butter, and vanilla; pour over oats. Top with slices of banana. Bake for 30-40 minutes until the top has browned.