Make the cake: Preheat the oven to 350 degrees F. Grease an 8 inch pyrex pan. Mash or puree the avocado's. You do not want any clumps, none!
Whisk the all-purpose flour, whole-wheat flour, cocoa powder, baking powder, baking soda and salt in a large bowl. In another bowl, whisk the avocado puree, brown sugar, eggs, greek yogurt, vegetable oil and vanilla. Fold the wet ingredients into the dry ingredients until just combined (it's fine if there are a few lumps).
Pour into the prepared dish and bake for 20 to 30 minutes. You want to remove this on the earlier side. When the cake is cooked, but on the underdone side. Let cool 10 minutes.
Using a spoon scoop the cake into a large bowl and crumble into pieces. You want to do this well the cake is still pretty hot. Then add the cream cheese. Mix until the cream cheese is combined and there is no white streaks.The cake will be moist and packable. Add the 1/2 cup semi-sweet chocolate chips and stir unti just combined.
Line two baking pans with wax paper. Roll the cake into 1 1/2-inch balls. Cover with plastic wrap and chill for several hours in the refrigerator, or place in the freezer for about 20 minutes. You want the balls to be firm but not frozen.
In a microwave safe bowl microwave the dark chocolate in 30 second intervals stirring each time until melted.
Remove the balls from the fridge. Place one ball at a time in the dark chocolate. Using a fork coat the balls in chocolate and then lift out and shake off any excess chocolate. Place back on the waxed lined baking sheet. Repeat with remaining balls.
Place back in the fridge for 10 to 20 minutes to help the chocolate harden faster.
Store these in the fridge or in a cool dark place.