Stir together in a mixing bowl the all-purpose flour, pecans, granulated sugar and melted butter until well combined and no dry pockets of flour remain.
Transfer to a 9x13 baking dish and firmly press the crust mixture into an even layer. A piece of parchment paper can help it to keep from sticking to your hands while pressing.
Bake for 15 minutes. Remove the baked crust layer from the oven and allow to cool on the counter for 15-20 minutes or until cool to the touch before adding remaining layers. While the crust cools, prepare the cream cheese layer.
Beat the cream cheese and sifted powdered sugar on medium-high speed, using a handheld mixer, for 1-2 minutes or until smooth and fluffy. Beat in the lemon zest, lemon juice, and vanilla extract just until combined. Set aside.
To a separate mixing bowl, add the instant lemon pudding and whole milk. Whisk for 2-3 minutes or until smooth and slightly thickened. Cover with plastic wrap and let sit for 5-10 minutes to fully thicken.
Once the crust has cooled, use a small offset spatula to spread the cream cheese mixture into an even layer.
Spread the lemon pudding layer evenly over the cream cheese layer, being careful not to mix the two layers. Then spread the whipped topping evenly over the pudding.
Cover the lemon lush dessert with plastic wrap and refrigerate for a minimum of 3 hours, or up to overnight, to allow the layers to chill and fully set before slicing and serving.
Before serving, garnish each slice with a sprinkle of fresh lemon zest and a thin lemon slice, if desired.
Notes
If your brand of instant lemon pudding is a dull yellow color once whisked with the milk, you can whisk in 2-3 drops of yellow gel food coloring to achieve a brighter yellow color.