Grease a 6-inch springform pan with cooking spray or butter. Alternatively, line a 6-inch cake pan with parchment paper.
In a large mixing bowl, add the bananas and mash until smooth. Add 3/4 cup of the coconut sugar, eggs, coconut oil, Greek yogurt, and vanilla. Mix until smooth. Add the flour, baking soda, baking powder, salt, cinnamon, and nutmeg, and mix until just combined. A few streaks of flour is fine.
Transfer the batter into the greased cake pan. Sprinkle with the remaining one tablespoon of coconut sugar and walnuts, if using.
Place the cake pan in the air fryer and air fry for 30 minutes, or until a toothpick comes out mostly clean. Check at the 15-minute mark- if the top is browning too quickly, loosely tent it with foil.
Remove the banana bread from the air fryer and let it cool in the pan for 15 minutes, then transfer it to a wire rack to cool.
Notes
TO STORE: Leftover banana bread will keep well at room temperature in an airtight container with a paper towel for up to 2 days. The paper towel keeps it super moist. If you don't think you'll finish it in 2 days, keep it in the fridge for one week. TO FREEZE: Place slices of the cooled banana bread in Ziploc bags and freeze for up to 2 months. Let the slices thaw in the fridge overnight or at room temperature for 2 hours.