Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners or grease with cooking spray.
In a large mixing bowl, combine the rolled oats, whole wheat flour, brown sugar, baking powder, baking soda, and salt. Mix well.
In a separate bowl, whisk together the milk, melted coconut oil, applesauce, and vanilla extract until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix, as this can result in dense muffins.
Gently fold in the berries or any other add-ins you desire.
Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full.
Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and let them cool in the tin for a few minutes before transferring them to a wire rack to cool completely.