1 cup green or red Swiss chard, stemmed and finely chopped
1 garlic clove
1/4 teaspoon coarse sea salt
1 cup Greek yogurt (whole)
1 tablespoon extra-virgin olive oil
1 tablespoon fresh lemon juice
1/8 teaspoon cayenne pepper
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.
Tzatziki can be refrigerated in an airtight container up to 1 week.