Preheat the oven to 350 degrees and put a rack on the middle shelf. Butter and flour a 9 by 5 by 3-inch loaf pan.
In a small bowl, combine the cinnamon and sugar for the cinnamon swirl filling. Set aside.
In a large bowl, whisk together the flour, baking soda, baking powder and salt.
In a separate small bowl, mash the bananas with a fork or wooden spoon, leaving a bit of texture.
In another large bowl, use a hand electric mixer or stand mixer to cream the 1/2 cup of butter and sugar together until light and fluffy.
Add the eggs, 1 at a time. Stir in the mashed bananas, sour cream and vanilla and beat until just combined. Add the dry ingredients and gently stir in pecans.
Pour half the batter into prepared pan (about 2 cups).
Sprinkle the cinnamon-sugar mixture evenly over the batter in pan.
Pour the rest of the batter over the cinnamon-sugar batter, carefully as to not mix batter with filling.
Bake for 1 hour and 10 minutes. Let cool for 5 minutes in the pan then turn out onto a wire rack to finish cooling and adding the glaze.
When banana bread is completely cooled, combine the powdered sugar, vanilla, and one tablespoon of milk. Whisk till smooth and thin enough to drizzle over bread. If glaze is too thick, add the additional tablespoon of milk (a little at a time) until it's the desired consistency.