Combine ground graham crackers, ground walnuts and powdered sugar in a large mixing bowl and mix together.
In a separate bowl, combine bananas, orange zest, and orange juice.
Slowly add and stir the banana mixture to the crackers mixture, adding just enough to moisten the dry ingredients.
Cover bowl loosely with plastic wrap and set in fridge for 30 minutes, or up to an hour.
Remove from fridge.
Place grated chocolate or cocoa powder in a shallow plate; set aside.
Shape cookie dough into bite size balls with your hands.
Roll each cookie in chocolate or cocoa until completely covered.
Set in fridge for at least 1 hour before serving. The longer they stand, the better they will taste.