Combine Greek yogurt, grated cucumber, minced garlic, lemon juice, chopped dill, salt, and pepper in a medium bowl. Mix until smooth and refrigerate for at least 30 minutes.

Heat olive oil in a large skillet over medium heat. Add chopped onion and sauté until translucent, about 5 minutes. Add minced garlic, then ground beef, oregano, smoked paprika, cumin, salt, and pepper. Cook until beef is browned, about 8 to 10 minutes.

Cook rice or quinoa according to package instructions and set aside.

Divide rice or quinoa among four bowls. Top each with seasoned ground beef.

Add halved cherry tomatoes, sliced red onion, kalamata olives, and crumbled feta on top of beef.

Spoon chilled tzatziki over each bowl and garnish with fresh parsley.