Add the ice cream to a food processor and pulse to the consistency of soft-serve ice cream. Transfer the ice cream to a bowl and return to the freezer while you make the cherry slush.
Wash out the food processor bowl and add the cherry drink mix, lime zest, 4 cups ice and 1/2 cup cold water. Process until smooth, adding more ice or water to adjust for desired consistency; for me, the icier the better.
To assemble the glacier:
Remove the glasses from the freezer and fill each halfway with cherry slush. Add 2 scoops of the vanilla ice cream to the center of each glass, pressing down to allow the slush to push up the sides of the glass. Top with more cherry slush and serve immediately. I like to serve these with a spoon and straw.