Preheat the oven to 325°F and grease a muffin tin or line with muffins cups.
In a medium bowl, combine the dry ingredients: whole wheat flour, oats, baking soda, salt and cinnamon.
In a large bowl, beat the coconut oil and maple syrup together with a whisk. Add the eggs and beat well. Mix in the mashed bananas, milk, and vanilla extract.
Stir the dry ingredients with the wet ingredients using a wooden spoon, just until combined. Fold in the nuts.
Divide the batter evenly between the muffin cups, filling each cup about two-thirds full. Sprinkle the tops of the muffins with oats and sugar, if desired.
Bake in the preheated oven for 22 to 25 minutes, or until a toothpick inserted into a muffin comes out clean. Allow them to cool in the muffin tin for 5 minutes. Then transfer from the tin to a wire rack for 10 minutes.