Mix the pistachio pudding mix and the undrained pineapples in a medium bowl.
Stir in the marshmallows and nuts.
Gently fold in the whipped topping.
For best results, chill for 4 hours before serving.
Notes
I love to use homemade whipped topping for this recipe. However, because of time, I do use Cool Whip sometimes.This can be served after chilling for 1 hour. But it is much better when chilled for at least 4 hours.