Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners.
In a bowl, combine rolled oats and milk. Let sit for 10 minutes until oats soften.
In another bowl, whisk together honey, oil, egg, and vanilla extract.
Add the wet ingredients to the softened oats and mix well.
In a separate bowl, mix whole wheat flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture and stir until just combined.
If using, gently fold in the berries.
Divide the batter evenly among the muffin cups.
Bake for 20-25 minutes or until a toothpick inserted into the center comes out clean.
Allow muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.