Preheat the air fryer to 300°F (150°C) for about 3 minutes. If your model does not require preheating, you can begin with the first batch immediately.

Peel the bananas and slice them into rounds about 1/8 inch (3 mm) thick. A mandoline makes it easier to keep the slices uniform, but a sharp knife works well too. Thicker slices will remain softer and require more drying time.

In a small bowl, combine the 1 teaspoon granulated sugar and 1/2 teaspoon ground cinnamon. Stir until evenly blended.

Arrange the banana slices in a single layer on a tray or plate. Lightly brush or toss them with the 1 teaspoon lemon juice, then lightly coat them with the 1 teaspoon neutral oil. Sprinkle the cinnamon-sugar mixture evenly over both sides, using the mixture as evenly as possible.

Place the banana slices in the air-fryer basket in a single layer, leaving a little space between slices. Work in batches if necessary. Do not pile the slices on top of one another because overlapping traps moisture and prevents even drying.

Air fry at 300°F (150°C) for 10 minutes. Carefully flip the slices with a thin spatula or tongs, then continue cooking for another 8 to 10 minutes.

During the final minutes, check frequently: The banana slices should look noticeably drier, with golden-brown edges and a deeper golden color. If the edges are browning too quickly while the centers remain soft, reduce the temperature to 275°F (135°C) and continue cooking in 2- to 3-minute increments.

Transfer the cooked banana chips to a wire rack and let them cool for at least 15 minutes. They will become firmer as they cool. If they are still noticeably soft after cooling, return them to the air fryer at 275°F (135°C) for 2 to 4 minutes, then cool again.

Once completely cool, serve the banana chips immediately or transfer them to an airtight container.