In a large mixing bowl, mix the pistachio pudding mix with the juice from the crushed pineapple. Whisk it until there is no more clumps of powder remain.
Next using a rubber spatula gently fold in the Cool Whip or homemade whipped cream until combined. Do not overmix, as doing so will make the consistency denser than it should be.
Then, to the pudding and whipped cream mixture, add the crushed pineapple, mini marshmallows, and chopped pecans; fold carefully until combined.
Cover and chill in the refrigerator for 4-6 hours, or overnight, for a more flavorful salad. This will allow the marshmallows to soften and really soak up the flavor.
