Preheat the oven to 350°F (175°C). Line a muffin tin with parchment liners.
Mix wet ingredients: Mash avocado until completely smooth. Whisk in eggs, maple syrup, and vanilla.
Mix dry ingredients: In a separate bowl, whisk together flours, cocoa powder, baking soda, baking powder, and salt.
Gently fold dry ingredients into the wet mixture. Fold in chocolate chunks and chopped nuts.
Bake: Fill muffin cups about ¾ full. Sprinkle extra nuts on top. Bake for 18–22 minutes, until a toothpick comes out with moist crumbs. Cool completely.
Make frosting: Blend avocados until silky smooth. Add cocoa powder, sweetener, vanilla, and salt. Adjust sweetness to taste. Chill 15 minutes for the best texture.
Finish: Frost cooled muffins and garnish with nuts or a dusting of cocoa powder.