Preheat oven to 350F and grease a muffin tin.
In a medium bowl, mash bananas and measure out 3/4 cup. If you have any leftover mashed banana you can freeze it for a smoothie.
Place mashed banana into medium bowl along with the milk, vinegar, maple syrup, and vanilla. No need to stir it yet.
Melt the coconut oil in a small pot over low heat. Set aside.
In a large bowl, mix together the dry ingredients (flour, sugar, baking powder, cinnamon, salt, and baking soda).
Stir coconut oil into the wet mixture. Pour wet ingredients onto the dry ingredients and stir until just combined. Do not over mix.
Gently fold in the walnuts and then the blueberries, being sure not to over mix as this can result in dense muffins.
Spoon about a heaping 1/4 cup of batter into each muffin tin, filling each tin about 3/4 full. I like to press a few extra blueberries on top of each so they look great after baking.
Bake at 350F for 23-27 minutes until a toothpick comes out clean.
Cool in pan for 5-8 minutes and then transfer muffins to a cooling rack and cool for another 15 minutes.