Line a 9x9” pan with foil and spray with cooking spray. Preheat oven to 350 degrees.
Place avocado in the bowl of an electric mixer fitted with the paddle attachment. Beat until the large pieces are all smooth. Add the cake mix and egg and beat until combined. (There may be a few pieces of avocado left, that’s okay.)
Place half the batter in the bottom of the pan. Spray your hands with cooking spray and press to flatten and cover the pan.
Sprinkle chocolate chips and nuts over bottom later. Pour sweetened condensed milk evenly over chips and nuts.
Place drops of the rest of the cake batter on top of the milk layer. Spray your hands again and press to evenly cover the top of the bars.
Bake for about 25-28 minutes, until a toothpick on the edges comes out clean. Cool completely before removing from pan.
Remove from pan, remove and discard foil. Slice into squares. Makes about 16 squares.