Preheat your oven to 350°F (175°C) to ensure that your muffins bake evenly.
Line your muffin tin with parchment paper liners or spray it with cooking spray to prevent sticking.
In a large mixing bowl, mash the ripe bananas with a fork until smooth. Add the milk, eggs, vanilla extract, and peanut butter. Whisk until creamy.
In another bowl, combine the oats, baking powder, baking soda, salt, and cinnamon (if using). Stir until evenly mixed.
Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.
If using, fold in the golden monk fruit sweetener and ¾ cup of the sugar-free chocolate chips.
Spoon the batter into the muffin tin, filling each cup about ¾ full. Sprinkle the remaining chocolate chips on top.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and let cool in the tin for 5 minutes before transferring to a wire rack to cool completely.