Preheat the oven to 350°. Cut a piece of parchment paper to fit the bottom of a 9" pan. Spray the bottom and sides of pan with vegetable spray. Place the parchment paper in the bottom of the pan and spray again. Set aside.
In a large bowl, sift togethr the flour, cornmeal, sugar, brown sugar, baking powder, baking soda and salt. Set aside.
Use a microplane to zest the lime. Reserve 1/4 teaspoon of zest for the glaze. Add the remainder to the flour mixture and whisk together to combine.
In a small bowl, whisk together the cooled, melted butter, buttermilk, eggs and vanilla.
Make a well in the dry ingredients and pour the wet ingredients into the well. Use a rubber spatula to fold the wet and dry ingredients together until just moistened, but do not beat.
Add the chopped mango and fold it evenly into the cake batter. Pour the batter into the prepared pan. Place the pan in the centef of the oven and bake for 30-40 minutes or until a cake tester comes out clean. Let the cake rest for about 10 minutes before turning it out onto a cake platter to continue cooling.
Make The Lime Glaze
In a small bowl, combine the powdered sugar, milk, reserved lime zest and juice of half a lime. Whisk together until well combined.
Spoon the glaze over the top of the cake and smooth over the edges with an offset spatula.