In an otherwise traditional tzatziki, a Greek dip made with yogurt, Swiss chard stands in for cucumber, adding a wealth of nutrients; whole-wheat pita wedges bring fiber to the hors d'oeuvre.
Prepare an ice bath; set aside. Bring a large saucepan of water to a boil. Add chard; cook until just tender, 3 to 5 minutes. Drain. Immediately plunge into ice bath to stop the cooking. Drain.
Using a mortar and pestle, grind garlic and salt into a paste. Stir chard, yogurt, garlic paste, oil, lemon juice, and cayenne pepper in a medium bowl. Serve with pita wedges.