Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with liners or lightly grease. I use a silicone cupcake tin.
In a large bowl, mash the ripe bananas. Add eggs, Greek yogurt, maple syrup, melted butter, and vanilla extract. Whisk until smooth.
In a separate bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt.
Gently stir dry ingredients into the wet mixture until just combined. Do not overmix.
Fold in chocolate chips if using.
Divide batter evenly into the muffin cups (about ¾ full).
Bake for 18–22 minutes, or until a toothpick comes out clean or with a few moist crumbs.
Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.