In a medium saucepan, mix together pudding mix and milk. Stir continuously and bring mixture to a boil, when mixture should thicken. Remove from heat and allow to cool to room temperature (you can continue stirring to speed up this process).
While pudding cools, melt the chocolate in a small microwave safe bowl or in a small pot.
Once the pudding has cooled, in a large bowl, gently fold together the whipped topping, pudding, and chocolate, until combined. (Now would be a good time to test the mixture -- you may prefer to add more chocolate for a more intense chocolate flavor).
Divide the mixture between two prepared pie crusts.
In a small bowl, combine peanut butter and flaxseed until smooth. Drizzle over the top of the pies. Swirl with a knife to create a design, if desired.
Top with additional chocolate chunks or chopped peanut butter cups, if desired.
Cover pies with a lid that does not touch the pies’ surface. Chill pies in freezer for 4-6 hours before serving.