Preheat your oven to 350°F (175°C).
Line your muffin tin with paper liners or grease it lightly with butter.
In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
In a large mixing bowl, beat butter and sugar until light and fluffy. Then add mashed bananas, apple sauce, egg whites, and vanilla extract. Mix until well combined.
Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.
Fold in the chocolate chips.
Evenly distribute the batter into the muffin tin, filling each cup about 2/3 full.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for about 5 minutes, then transfer to a wire rack to cool completely.