Preheat oven to 175°C (350°F) and grease a 12-cup muffin tin or line with paper liners.

In a large mixing bowl, combine mashed bananas, maple syrup, egg, Greek yogurt, and vanilla extract, whisking until the mixture is homogeneous.

In a separate bowl, sift together whole wheat flour, cocoa powder, baking soda, and salt.

Gently fold the dry ingredients into the wet mixture using a spatula until just combined; do not overmix to avoid a dense texture.

Stir in 1/4 cup of the dark chocolate chips.

Apportion the batter evenly into the prepared muffin tin, filling each cup approximately three-quarters full.

Top with the remaining chocolate chips.

Bake for 18 to 22 minutes or until a toothpick inserted into the center of a muffin comes out clean.

Cool in the pan for 5 minutes before transferring to a wire rack for complete thermal stabilization.