Cut the avocados in half, remove the pits, and scoop the flesh into a medium bowl.

Add the feta, Greek yogurt, garlic, lemon juice, olive oil, cilantro or parsley, salt, black pepper, and red pepper flakes if using.

Mash everything together with a fork or potato masher until creamy but still slightly chunky. Stir in the red onion if using.

Taste and adjust the seasoning with more salt, pepper, or lemon juice as needed.

Serve immediately with tortilla chips, pita chips, fresh vegetables, or crackers.