Step 1: Preheat your oven to 350°F (175°C).
Step 2: Grease your muffin tin or line it with muffin liners.
Step 3: In a large bowl, whisk together flour, sugar, cocoa powder, salt, and baking soda.
Step 4: In another bowl, mash the ripe bananas, then mix in the egg, applesauce, and vanilla.
Step 5: Pour the wet mixture into the dry ingredients and fold until just combined.
Step 6: Spoon the batter into the muffin tin, filling each cup about two-thirds full.
Step 7: Bake for 18-20 minutes or until a toothpick comes out clean.
Step 8: Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack.