Line a small tray or plate with foil.
Wash, dry and peel the lemon and lime using a vegetable peeler or zester. Stack the peels on top of each other and slice into tiny strips. Next, slice the strips the other direction, creating a tiny dice. Place diced peel on the foil-covered tray and allow to dry overnight, uncovered. The next day the zest should be dried out, yet still retain its vibrant color. If it is not yet completely dried, allow more time.
Add 1 tablespoon of each type of dried peel and the cumin to the salt and stir to combine.
Place into pretty jars for storage—or gifting.