Sliced and cut mango into chunks. Place in a food processor or blender and puree till smooth.
In a medium bowl combine the condensed milk, key lime juice (if you like a bit more tang then add the 2/3 cup of juice if you like it more mild then just use 1/2 cup), mango puree, and cool whip till blended. You can use a whisk or hand held beaters on low.
Pour the mixture into a 9 inch shortbread or graham cracker crust. Cover and refrigerate for at least 4 hours. When ready to serve sprinkle the lime zest on top and garnish with some whipped cream and a thin lime slice.