In a large bowl, combine the ground beef or lamb, grated onion, minced garlic, chopped parsley, breadcrumbs, egg, cumin, paprika, salt, black pepper, and red pepper flakes (if using). Mix until just combined; do not overmix.

Shape the mixture into small meatballs, about 1 to 1.5 inches in diameter. You should get around 20 meatballs.

Heat olive oil in a large skillet over medium heat. Once hot, 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 mixing the Greek yogurt, lemon juice, minced garlic, and salt in a small bowl. Adjust salt to taste.

Once the meatballs are done, remove them from the skillet and serve hot with the yogurt sauce drizzled on top or on the side. Garnish with fresh parsley.