Prepare the Glass: Rub the lime wedge around the rim of your serving glass. Pour the coarse salt onto a small plate and dip the rim of the glass into the salt to create a salted rim. Set the glass aside.
Blend the Ingredients: In a high-speed blender, combine the frozen mango chunks, water or orange juice, fresh lime juice, and optional agave or simple syrup.
Blend Until Smooth: Blend on high speed until the mixture is completely smooth and has a slushie-like consistency. If using fresh mango, add a handful of ice cubes to the blender to make it frosty.
Pour and Serve: Pour the virgin margarita mixture into the prepared glass. Garnish with a fresh lime wedge and a slice of mango on the rim, and serve immediately.
Notes
For a sweeter flavor, you can use a bit of orange juice in place of the water.