For the crust: Preheat the oven to 350 degrees F. Line a 9-by-13-inch baking pan with parchment paper and grease with vegetable oil.
In a medium bowl, sift the flour, granulated sugar and salt. Add the butter to the dry ingredients and mix with a spatula or spoon. Press the crust mixture into the bottom of the prepared pan. Bake until the crust is lightly browned, about 10 minutes. Let cool slightly.
For the filling: Blend the mango with 2 tablespoons water in a blender.
Beat together the granulated sugar and eggs in a bowl until combined. Stir in the lemon zest and juice and mango puree. Stir in the flour.
Pour the filling over the crust. Lower the oven temperature to 325 degrees F and bake until the filling is set, about 25 minutes. Let cool, then refrigerate at least 1 hour before cutting the bars.
For the topping: Dust the bars with powdered sugar, sprinkle with toasted coconut and enjoy!