In a large bowl, add the mashed potato, and lemon juice. In another bowl, cream the brown sugar, white granulated sugar, and room-temperature butter, and mix well. Slowly fold in the egg, and vanilla extract, and mix well.
In a separate large mixing bowl, add the flour, baking soda, baking powder, ground cinnamon, and kosher salt, and mix well.
Slowly pour the dry batter into the wet batter, and mix well. Slowly add in the buttermilk, and add your walnuts if using.
Spray your mini loaf pans with cooking spray, and then pour the batter into the prepared pans, filling about 2/3 the way full. Set the baking pans into the air fryer basket and set the cooking time for 12-15 minutes at 320 degrees F, using the air fryer setting. For best results check your banana cake frequently as it cooks up.
In a large mixing bowl, add the cream cheese, butter, and cream together, until light and fluffy. Then slowly add in the vanilla extract, lemon juice, and lemon zest mix well, and slowly fold in the powdered sugar.
Mix until you get the desired consistency. Spread over the banana cake, and refrigerate until serving.