Cut the avocado in half, remove the pit, and scoop the flesh into a medium bowl.
Mash the avocado with a fork until mostly smooth, leaving a little texture if desired.
Add the Greek yogurt, lime juice, garlic, cilantro, cumin, salt, black pepper, and red pepper flakes.
Mix until smooth and creamy. Taste and adjust the seasoning with more salt or lime juice if needed.
Transfer the dip to a serving bowl and garnish with cilantro, diced avocado, and chili flakes if desired.
Serve immediately with tortilla chips, pita bread, crackers, or fresh vegetables.