In a large mixing bowl, combine flour, protein powder, cocoa powder, sea salt, granulated sweetener of choice and mix well. Add in the mashed banana- Mixture should be very crumbly. Add the chocolate chunks and walnuts and mix well. In a microwave safe bowl, melt the nut butter. Pour wet mixture into the flour/banana mixture until fully incorporated. Using a tablespoon at a time, add the dairy free milk of choice until a very thick batter is formed. Using your hands, form into bite sized balls and refrigerate for at least 20 minutes to firm up.