Preheat your outdoor grill to high heat and brush the grills with a little bit of oil, if necessary.
Combine the chopped parsley, onion and garlic in a small food processor and process until really finely chopped, almost paste-like. You could also do this with a knife; just make sure that all the ingredients are chopped super finely.
In a large mixing bowl, combine the ground lamb, ground beef, finely chopped parsley onion and garlic, salt, white pepper, smoked paprika, allspice, nutmeg and cardamom; knead well with your hands until all the ingredients are well combined; form the meat mixture into 8 thin, elongated patties.
Once the grill is super hot, place the patties on the grill, close the lid and cook for about 5 minutes, or until the meat easily detaches from the grill, then flip and cook the patties for another 3 to 5 minutes, or until the meat is nicely charred, cooked all the way through and its juices run clear.
Remove the meat to a clean plate and serve with a drizzle of tahini paste and a handful of parsley, if desired.