Preheat the oven to 350 F. Grease a 9x5 inch loaf pan with baking spray. In a large mixing bowl, whisk together flour, baking soda and salt. Set aside.
In another bowl, pour butter, the egg and the sugars. Use a wire whisk and beat until combined and smooth. Add the sour cream, mashed banana and vanilla extract. Beat with the wire whisk until the ingredients are incorporated and the mixture is uniform in color.
Add the wet mixture to the flour mixture, Use the whisk to mix the two, just until the mixture is combined. Do not overmix. This is a thick batter. Switch to a rubber spatula and fold in the chocolate chips.
Drop half of the batter in dollops all over the surface of the loaf pan, then use an offset spatula to smoothen and even it out. Sprinkle the cinnamon sugar swirl mixture over the batter, reserving about 1 tbsp.
Again, drop the remaining batter in dollops over the cinnamon, then use the offset spatula to even it out. Sprinkle the remaining cinnamon mixture over the cake batter.
Use a knife to make one swirling motion in the batter, being careful not to scrape the bottom surface of your pan to avoid damage to it. Bake the quick bread at 350 ℉ for 55-60 minutes, or until a toothpick inserted at the center comes out clean. You can tent the loaf pan with foil during the last ten minutes of baking to avoid overbrowning.
Let the pan cool on a wire rack for about an hour. Then, remove the cake by first gently pressing down the sides, and/or loosening the sides with a wooden spoon or knife. Let the bread cool completely, or cool enough before slicing.