Preheat oven to 425 °F (218 °C). Line a muffin pan with muffin liners and lightly spray them with cooking spray. Set aside.
In a large bowl, mix together bananas, maple syrup, vanilla extract, egg, coconut oil, and greek yogurt. Set aside.
In a medium bowl whisk together flour, baking soda, cocoa powder, and salt.
Carefully pour in the dry ingredients into the wet ingredients and mix until just incorporated and no flour is left at the bottom.
Fold in the chocolate chips.
Using a large cookie scoop (or ice cream scoop), fill the muffin cups 3/4 full and add additional chocolate chips on top, if desired. Repeat until all the batter is used up. You may get more than a dozen, that's okay.
Bake for 5 minutes at 425 °F (218 °C) then turn down the oven to 375 °F (191 °C) and finish baking for 12 minutes, or until a toothpick inserted into the center of the muffin comes out clean.
Remove from oven and let cool in the muffin pan for 5 minutes before transferring to a wire rack to cool completely.
Store in an airtight container for up to 5 days.
Notes
Baking at a high temperature initially gives your muffins a "lift" and that glorious bakeshop muffin top. It essentially gives the baking soda and ingredients a boost of heat in the beginning.