In a medium bowl, mash the ripe bananas with a fork until very smooth and creamy.

Add the egg to the mashed bananas and whisk until fully combined.

Stir in the oat flour a little at a time until a soft, sticky dough forms that holds its shape.

Mix in the melted coconut oil until the dough is evenly moistened.

If the dough is too wet to handle, sprinkle in a small amount of additional oat flour until it is just firm enough to scoop.

Lightly grease the air fryer basket with a thin layer of coconut oil or line it with air fryer safe parchment.

Scoop walnut sized portions of dough and place them in the basket, then gently flatten each portion into a small disc about 1.25 centimeter thick.

Arrange the treats in a single layer with space between each piece to allow air to circulate.

Air fry at 180 °C (350 °F) for 15 to 20 minutes, turning the treats once halfway through cooking.

Begin checking at 15 minutes; the treats are done when the tops and bottoms are lightly golden and feel firm to the touch.

Transfer the treats to a rack and let them cool completely to room temperature before serving to your dog.

Store cooled treats in an airtight container at room temperature for up to 3 days, in the refrigerator for up to 7 days, or freeze for up to 3 months.