Preheat the oven to 375°F (190°C) and grease a baking dish.
In a bowl, mix brown sugar, flour, and softened butter until crumbly. Stir in oats and pecans, then set aside.
In another bowl, whisk flour, sugar, and milk until smooth. Add melted butter and mix well.
Pour the batter into the prepared dish.
Arrange sliced bananas evenly on top.
Sprinkle the streusel topping over the bananas.
Bake for 45–50 minutes until golden brown and set.
Let cool slightly before serving.
This banana cobbler recipe is best served warm.