In a large bowl, combine the ground meat, grated onion, minced garlic, chopped parsley, breadcrumbs, egg, cumin, paprika, salt, black pepper, and red pepper flakes (if using). Mix until well combined.
Shape the mixture into small meatballs, about 1 inch in diameter. You should have approximately 20 meatballs.
Heat the olive oil in a large skillet over medium heat. Add the meatballs in batches, being careful not to overcrowd the pan. Cook for about 5-7 minutes, turning occasionally, until browned on all sides and cooked through.
While the meatballs are cooking, prepare the yogurt sauce by combining the Greek yogurt, lemon juice, minced garlic, and salt in a small bowl. Mix well and set aside.
Once the meatballs are cooked, remove them from the skillet and drain on paper towels.
Serve the meatballs warm, drizzled with the yogurt sauce and garnished with fresh parsley.