In a large mixing bowl, combine Greek yogurt, lime juice, garlic powder, salt, and pepper to make the dressing.
Fold in the shredded chicken until well coated.
Add corn, black beans, onion, avocado, and cilantro. Stir gently to combine.
Taste and adjust seasoning. Add cotija cheese if desired.
Serve chilled on tostadas, in wraps, or with lettuce cups.
