In a medium mixing bowl, whisk together the instant vanilla pudding mix and the cold whole milk. Whisk vigorously for about 2 minutes until the mixture begins to visibly thicken. Place the bowl in the refrigerator for at least 15 minutes to set completely firm.

Pour the chilled heavy whipping cream into a large, cold mixing bowl. Using an electric mixer on medium-high speed, beat the cream until soft peaks begin to form. Add the powdered sugar and continue beating until you reach stiff, structured peaks.

Remove the set pudding from the fridge and use a spatula to roughly chop it into bite-sized chunks. Gently fold these pudding chunks and the mini marshmallows into the whipped cream using a sweeping bottom-to-top motion.

Slice your fresh bananas into thick coins and toss them lightly in lemon juice. Mound the fluff mixture into a shallow white ceramic bowl. Arrange the banana slices over the top and rain the crushed vanilla wafer crumbs over the entire mountain. Serve immediately or chill for 1 hour.