Begin by preheating your oven to 350°F (175°C). Prepare a muffin tin by placing paper liners in each cup or light greasing with cooking spray to prevent sticking.
In a medium mixing bowl, combine the well-mashed bananas with the melted coconut oil. Stir thoroughly until the mixture is smooth and well blended.
Next, add the packed brown sugar, egg, and pure vanilla extract to the banana mixture. Mix until everything is seamlessly incorporated and the batter appears smooth.
Carefully sprinkle the baking soda and fine salt over the mixture, then stir gently to ensure the dry ingredients are evenly distributed without overmixing.
Gradually add the all-purpose flour to the bowl, folding it in with a spatula or wooden spoon just until no visible flour remains; avoid excessive stirring to keep the muffins tender.
If you're including walnuts, gently fold in the chocolate chunks and optional walnuts, ensuring they are evenly dispersed throughout the batter.
Use a scoop or spoon to fill each muffin cup about 3/4 full with the batter, allowing space for the muffins to rise as they bake.
Place the muffin tin in the preheated oven and bake for approximately 18-20 minutes. They are done when a toothpick inserted into the center of a muffin comes out clean or with a few moist crumbs.
Once baked, allow the muffins to cool in the pan for about 5 minutes. Then, transfer them carefully to a wire rack to cool completely.
Notes
Arrange the muffins on a beautiful platter, dust with powdered sugar, and serve with fresh banana slices.