Peel the bananas and slice them into thin rounds, about 1/8 inch thick.
In a bowl, toss the banana slices with lemon juice to prevent browning. If desired, sprinkle cinnamon over the slices and toss to coat evenly.
Preheat the air fryer to 350°F.
Lightly spray the air fryer basket with cooking spray or brush with a small amount of oil to prevent sticking.
Arrange the banana slices in a single layer in the air fryer basket, making sure they do not overlap.
Air fry the banana slices for 10-15 minutes, shaking the basket halfway through to ensure even cooking. Check for crispness; they should be golden and crispy.
Once done, remove the chips from the air fryer and let them cool completely on a wire rack. They will become crispier as they cool.