Preheat oven to 350⁰F/177⁰C. Grease and line a 9x5-inch rectangular pan with parchment paper.

Melt chocolate chips in a microwave for 15 minutes. Set aside.

In a bowl, mix together avocado and brown sugar until blended. Add egg, maple syrup and melted chocolate. In a separate bowl, sift together flour, cocoa powder, salt, and baking soda.

Combine sifted dry ingredients into the wet ingredients.

Fold chopped walnuts.

Pour mixture into prepared pan and level with a knife.

Bake for 30-40 minutes, or toothpick inserted in the center comes out nearly clean. Let it rest in baking dish for 5 minutes and cool further on a cooling rack.