Mix graham cracker crumbs with melted butter, sugar, and salt until it resembles damp sand. Press firmly into a 9-inch pie dish, covering the base and sides. Refrigerate for 15 minutes.
Beat softened cream cheese until completely smooth with no lumps, 2 to 3 minutes.
Add condensed milk and beat on low until combined. Add lemon juice, lemon zest, and vanilla. Beat until smooth.
In a separate bowl, whip cold heavy cream to firm peaks. Fold gently into the lemon mixture in three additions.
Pour filling into the chilled crust and smooth the top. Cover with plastic wrap and freeze for a minimum of 4 hours or overnight.
Before serving, whip cold heavy cream with powdered sugar and vanilla to medium-soft peaks. Spread or pipe over the frozen pie. Decorate with lemon slices and zest. Slice with a warmed knife and serve immediately.