In a medium mixing bowl, combine Greek yogurt, mayonnaise (if using), lime juice, garlic, sea salt, and onion powder. Stir until smooth.

Blend the creamy mixture using a hand mixer or food processor for 15-30 seconds until smooth.

Finely chop cilantro and fold it into the smooth sauce or pulse in the processor for a few seconds.

Adjust flavor and consistency by adding more lime juice or milk as needed.

Transfer the sauce to an airtight container and refrigerate for up to 5 days.