Preheat the oven to 180°C and line a muffin tin with paper cases or silicone moulds.
Mash the banana in a mixing bowl, then add the egg and oil and mix well.
Stir in the vanilla extract, cinnamon, and sugar or date syrup.
Add the oats, flour, and baking powder and mix until combined.
Pour in the oat milk and mix again. Add a little more if needed — the batter should be thick but pourable.
Gently fold in the blueberries.
Spoon the mixture into the prepared muffin tin.
Bake in the oven for about 25 minutes, until risen and lightly golden.
Alternatively, bake in an air fryer at 180°C for 15–20 minutes.
Remove from the oven and allow to cool on a wire rack before serving.