Preheat oven to 325 degrees.
In a medium mixing bowl combine the graham cracker crumbs, sugar, salt, and melted butter. Toss until crumbs are moist.
Press crumbs into a 9-inch oven-safe pie dish. Press up the sides to the edge or rim of the pie dish. Place in the oven and bake for 7 minutes, then remove and let cool.
In a medium mixing bowl combine the condensed milk, lemon juice, lemon zest, and lemon oil or extract. Whisk to combine, set aside.
In the bowl of a stand mixer fitted with the whisk attachment add the heavy cream, powdered sugar, vanilla extract, food coloring (if desired), and salt. Mix on low and gradually work up to high. Whip until stiff.
Add condensed milk mixture and mix for 30 seconds on medium speed. Add the mascarpone and mix until combined, about 30-45 seconds on medium speed.
Pour filling into the cooled crust and spread into an even layer. Cover with plastic wrap and chill for at least 4 hours or overnight.
To garnish, top with whipped cream, fresh fruit and lemon slices, if desired. Keep chilled.