Whisk the pudding mix and cold milk in a large bowl for 2 minutes.
Pour in the sweetened condensed milk and vanilla extract.
Whisk again until the mixture looks smooth and slightly thicker.
Fold in the whipped topping until no streaks remain.
Let the filling sit for 5 minutes to thicken.
Slice the bananas into coins about 1/4 inch thick.
Toss the banana slices gently with the lemon juice.
Spread a thin layer of pudding in a 9x13-inch dish or deep 3-quart bowl.
Add a single layer of vanilla wafers.
Place banana slices in an even layer.
Spoon more pudding on top and smooth it gently.
Repeat the layers until everything is used.
End with pudding on top.
Cover the dish tightly.
Chill it for at least 4 hours.
Add crushed wafers or extra whole wafers right before serving.