Preheat oven to 400°F. Spray each muffin cup with cooking spray.
Place oats in a blender and blend until they begin to look like flour. Pour into a bowl and add milk. Allow to sit and soak for 15 minutes.
Meanwhile, mash the bananas in a bowl with the sugar. Add eggs, honey, and vanilla, and whisk together.
Heat coconut oil just until melted (avoid over-heating), then set aside to slightly cool (this will help to prevent the coconut oil from clumping once added to colder ingredients).
In a separate bowl, mix together flour, baking soda, baking powder, cinnamon and salt.
Add oats to the bananas and blend well; stir in the oil.
Pour the wet ingredients into the dry and mix until just combined; avoid over mixing (this can cause the muffins to be tougher and more dense). Fold in chopped walnuts (or sprinkle on top of muffins just before baking).
Scoop an even amount of batter into each muffin cup, and bake for 24-28 minutes until a toothpick inserted comes out clean.
Allow to cool for 5-10 minutes before serving.