If preparing a crust from scratch, stir together 1½ cups of finely crushed graham crackers with ¼ cup granulated sugar and 6 tablespoons of melted butter. Press the mixture evenly into a 9-inch pie pan and place it in the refrigerator to firm while you make the filling.
Place the softened cream cheese into a large bowl and whip on medium speed using a hand mixer until it becomes completely smooth and free of lumps. Pause to scrape the sides of the bowl as needed.
Slowly stream in the sweetened condensed milk while continuing to beat the mixture. Blend until the texture becomes silky and homogeneous.
Add the thawed lemonade concentrate and, if desired, a bit of freshly grated lemon zest. Mix thoroughly until the filling thickens slightly and develops a bright, citrusy profile.
In a separate bowl, whip the heavy cream until soft peaks form. Gently fold the whipped cream into the lemon mixture to maintain its airy structure. Alternatively, if using whipped topping, incorporate it directly by folding until the mixture is uniform and streak-free.
Transfer the lemon cream filling into the prepared graham cracker crust, smoothing the surface with a spatula to create an even layer.
Cover the pie loosely with plastic wrap and refrigerate for a minimum of 4 hours, or until the filling is set and firm to the touch.
Before serving, decorate the top with dollops of whipped cream and garnish with lemon slices or zest curls, if desired. Serve well chilled.