Preheat oven to 350°F (175°C). Mix flour, melted butter, and chopped pecans. Press into a 9x13 baking dish.
Bake for 15 minutes or until lightly golden. Cool completely before layering.
In a bowl, beat softened cream cheese with powdered sugar until smooth. Spread evenly over the cooled crust.
Whisk together instant lemon pudding mix and cold milk until thickened. Spread over the cream cheese layer.
Top with whipped topping, spreading evenly across the pudding layer.
Refrigerate for at least 4 hours, preferably overnight, until fully set. Slice into squares and serve chilled.