Begin by preheating your oven to 350°F (175°C). Lightly grease a 9x9-inch baking dish and set it aside.
In a large mixing bowl, combine the well-mashed bananas with the melted butter, stirring until they are fully integrated.
Add the packed brown sugar to the banana mixture, followed by the egg and vanilla extract. Mix thoroughly until the batter is smooth and well-combined.
In a separate bowl, whisk together the baking soda, fine sea salt, ground cinnamon, and all-purpose flour. Gradually incorporate this dry mixture into the banana batter, stirring gently until just combined. If desired, fold the chopped walnuts into the dough for added texture.
On a lightly floured surface, carefully roll out the dough into a rectangle approximately 1/4 inch thick for even baking.
For the filling, use a spatula to evenly spread the softened butter over the rolled-out dough. In a small bowl, combine the brown sugar and ground cinnamon, then evenly sprinkle this mixture over the buttered surface of the dough.
Starting from one edge, tightly roll the dough into a log shape. Once rolled, slice the log into 1-inch thick rolls for even baking.
Place the cinnamon rolls into the prepared baking dish with the cut side facing up, arranging them snugly.
Bake the rolls in the preheated oven for 25-30 minutes, or until they achieve a beautiful golden brown color.
While the rolls are baking, prepare the glaze by whisking together the powdered sugar, milk, and vanilla extract in a bowl until you achieve a smooth consistency.
As soon as the rolls are done baking, drizzle the glaze generously over the warm rolls while they are still in the dish, allowing it to seep into the crevices.
Notes
Serve warm, drizzled with extra glaze and garnish with fresh banana slices or chopped walnuts.