Preheat grill to medium-high heat.
In a large bowl, toss together beef, onion, olive oil, garlic powder, paprika, salt, and pepper.
Place beef and onion mixture on grill and cook for about 5-7 minutes, until beef is cooked to desired doneness and onions are tender.
Remove beef and onions from grill and set aside.
Grill flatbreads for about 1-2 minutes on each side, until lightly charred.
Spread Greek yogurt evenly on each flatbread.
Top with grilled beef and onions.
Sprinkle with chopped fresh parsley.
Serve immediately and enjoy!