Preheat the oven to 375°F.

In a 9-inch cast iron skillet, toss the sliced bananas with the melted butter, half of the brown sugar, and the cinnamon.

In a separate bowl, mix the oats, flour, and remaining brown sugar. Cut in the cold butter until the mixture is crumbly.

Sprinkle the oat crumble evenly over the bananas in the skillet.

Bake for 25 minutes until the topping is golden brown and the filling is bubbling.