Warm the water and agave syrup in a medium saucepan, stirring until syrup is dissolved. Remove from the heat and cool for 10-15 minutes.

Use a Microplane grater to get just the green part of the lime peels. You can also use a peeler and sharp paring knife or the fine side of a box grater for this step.

Set aside one teaspoon of the zest, add the remaining lime zest to the mixture.

Juice the limes and add the juice to the mixture. Stir in the tequila, then refrigerate until very cold.

Pour into an ice cream maker and follow the instructions to freeze it. If you do not have an ice cream maker, follow these directions to create an Italian-style ice or granita.

Pour out the salt and sugar onto a piece of waxed paper. Add the remaining lime zest. With the back of a spoon, rub the zest into the crystals until you smell the lime, this helps release the oils. Add the red pepper flakes and mix thoroughly. Serve in a small bowl with a spoon, allowing people to add as much as they like.