Preheat your oven to 350°F. Place the graham cracker crust on a baking sheet and bake for 5-7 minutes until lightly toasted. Remove from the oven and let cool completely.
In a mixing bowl, combine the mascarpone cheese, powdered sugar, and vanilla extract. Mix until smooth and creamy.
Spread the mascarpone mixture evenly over the cooled graham cracker crust.
In another bowl, toss the sliced peaches with lemon juice to prevent browning. Arrange the peach slices on top of the mascarpone layer.
Chill the tart in the refrigerator for at least 1 hour before serving to allow the flavors to meld.
Garnish with fresh mint leaves if desired, and slice into wedges to serve.