Prep the air fryer and dish: Preheat the air fryer to 350°F (175°C) for 3–5 minutes. Lightly grease a 6–7 inch round baking dish, cake pan, or 2–4 ramekins that fit in your air fryer basket.
Mix the wet ingredients: In a medium bowl, whisk the mashed banana, egg, milk, maple syrup, vanilla, and melted butter or coconut oil (if using) until smooth.
Add the dry ingredients: Stir in the oats, cinnamon, baking powder, and a pinch of salt until well combined.
The mixture will be pourable but thick.
Fold in blueberries: Gently fold in the blueberries. If using frozen, do not thaw; add them straight from the freezer to prevent bleeding.
Fill the dish: Pour the mixture into the prepared dish or divide among ramekins. Smooth the top with a spoon.
Air fry: Place the dish in the air fryer basket.
Cook at 350°F (175°C) for 14–18 minutes for a single dish or 10–14 minutes for ramekins. The oats are done when the top is set and lightly golden and a toothpick comes out mostly clean.
Rest briefly: Let it sit for 5 minutes to set. This helps the oats firm up while staying tender inside.
Serve: Enjoy warm as is, or top with a splash of milk, a dollop of yogurt, extra blueberries, or a drizzle of nut butter.