Dip the rim of a margarita glass in lime juice then margarita salt. Hold the glass upside down for 15 seconds for the salt to set. Fill the glass with ice.
Cut the peach into 4 slices and remove any remnants of the pit. Place the peach slices into a blender with the remaining ingredients and blend for 15 seconds. Pour the blended peach puree into the cocktail shaker. Add ice and shake for 10 seconds. Pour into the ice-filled glass.