Heat oven to 400 degrees F. Spray a 9x13 baking dish with baking spray.
Cut bananas lengthwise and lay into baking dish.
In a mixing bowl, combine remainder of filling ingredients (brown sugar, melted butter, rum, cornstarch, and cinnamon). Stir well and spread on top of bananas, covering evenly.
In a separate mixing bowl, combine topping ingredients (flour, brown sugar, cinnamon, dark rum, and softened butter). Use the back of a fork to thoroughly combine mixture (will be crumbly). Stir in pecans. Sprinkle topping over bananas/filling. Add more pecans on top if desired. Just be sure to cover baking dish with aluminum foil halfway through baking if you used a lot of pecans (to prevent them from burning).
Bake 35 minutes or until golden brown and bubbly. Allow to cool and serve with a scoop of ice cream or whipped topping.