1. Preheat an air fryer to 180 C (360 F). Spray a loaf pan with cooking spray.
2. Using an electric mixer, beat the sugar and butter together together in a bowl until creamy.
3. Mix together banana, egg, and honey in a separate bowl.
4. Fold in banana mixture into butter mixture until incorprated well.
5. Add the flour, cinnamon, and salt into the banana-butter mixture. Mix batter until blended and smooth. Fold in half of the walnuts. Transfer to the prepared loaf pan; level the top using the back of a spatula or spoon. Sprinkle with remaining walnuts.
6. Place the loaf pan in the air fryer basket.
7. Set the timer for 20 minutes or until a toothpick inserted into the center of the cake comes out clean. Let cool.