In a large mixing bowl, combine the instant vanilla pudding mix and milk. Whisk together until smooth and well combined. Let it sit for about 5 minutes to thicken slightly.
Gently fold in the whipped topping until fully incorporated.
Add the sliced bananas, crushed pineapple, and mini marshmallows to the bowl. If using, add the chopped pecans as well.
Stir everything together until evenly mixed.
Add the vanilla extract and mix gently to combine.
Cover the bowl with plastic wrap and refrigerate for at least 1 hour before serving to allow the flavors to meld and the salad to chill.
Serve chilled, and enjoy!