Preheat your oven to 375°F (190°C). Line a muffin tin with paper liners or grease it lightly.
In a mixing bowl, whisk together the all-purpose flour, baking soda, and salt. Set aside.
In a separate large bowl, mash the bananas until smooth.
Add the melted butter, granulated sugar, brown sugar, and vanilla extract to the mashed bananas. Stir until well combined.
Add the dry mixture to the wet ingredients, stirring gently until just combined.
Fold in the chocolate chunks (or chips) gently, being careful not to overmix.
Distribute the muffin batter into muffin cups, filling each cup about ⅔ full. Top with extra chocolate chunks.
Bake for 17-20 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for a few minutes before transferring them to a wire rack to cool completely.