Preheat your oven to 350°F (175°C) for even baking.
Line your muffin tin with paper liners or grease it lightly.
In a mixing bowl, whisk together the egg, smashed bananas, oat milk, and vanilla extract until smooth.
In another bowl, mix the rolled oats, sea salt, and maple syrup until coated.
Pour the wet mixture into the dry mixture and stir gently until just combined.
Fold in the mixed berries and chopped apple.
Spoon the batter into the muffin tin, filling each cup about ¾ full.
Bake for 20-25 minutes or until a toothpick comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.
