Preheat the oven to 350 degrees F. Line a muffin pan with paper liners and set aside.
In a medium bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon. Set aside.
Peel the bananas and mash with a fork. Place the mashed bananas in a large bowl. Add the brown sugar, coconut oil, almond milk, and vanilla extract. Stir until well combined. Slowly stir in the dry ingredients. Mix until just combined. Carefully fold in the blueberries.
Fill muffin liners three-quarters full. Sprinkle with turbinado sugar, if desired. Bake until toothpick inserted into center comes out clean, about 25 minutes. Transfer to wire rack to cool. Store, covered, at room temperature
These muffins freeze well. To reheat, place muffin in the microwave for about 30 seconds.
For a tree nut free muffin, replace almond milk with any dairy-free alternative and omit the walnuts.