Preheat your oven to 350°F (175°C).
In a medium bowl, combine the graham cracker crumbs, melted butter, and granulated sugar. Mix until the crumbs are evenly coated.
Press the mixture firmly into the bottom and up the sides of a 9-inch tart pan. Bake for 10 minutes, then remove from the oven and let cool.
In a blender, combine the diced mangoes, coconut milk, powdered sugar, vanilla extract, cornstarch, lime juice, and a pinch of salt. Blend until smooth.
Pour the mango mixture into the cooled crust.
Bake the tart for 25-30 minutes, or until the filling is set and slightly golden on top.
Allow the tart to cool to room temperature, then refrigerate for at least 2 hours before serving.
Garnish with fresh mint leaves if desired.