Soak 4 thick wooden skewers in water (You can also use metal skewers. If you use thin wooden skewers, the meat may be too heavy and will be difficult to handle).
In the bowl of a food processor, pulse the onion chunks until roughly chopped. Add the garlic cloves, pine nuts, parsley, cumin, cinnamon, cardamom, coriander, allspice, and black pepper. Pulse to combine until all ingredients are nicely chopped.
Transfer onion mixture to a large bowl. Add ground lamb, ghee, and Kosher salt and mix with your hands until just combined. Refrigerate for at least an hour.
When ready to cook, preheat a clean outdoor grill over medium-high heat (If you are using a grill pan, wait to heat until ready to cook). If using an oven, adjust rack to top position and preheat for 425°F.
Separate lamb mixture into 4 equal portions. Lightly spray cutting board with oil, then roll out each portion into logs. Press skewer into the log and pinch meat around the skewer to seal. Press to flatten skewer slightly. They should be about 8 inches long and 1 ½ inches wide.
if using an outdoor grill: Right before grilling, spray both sides of each skewer with avocado oil spray to prevent from sticking to the grill grates. Grill 4 minutes per side, until cooked through.
If using a grill pan: Heat over medium heat and spray with avocado oil. Cook skewers for 4 minutes per side, until cooked through.
If using an oven: Right before cooking, spray both sides of each skewer with avocado oil spray. Cook for 10-12 minutes, until cooked through.
Serve immediately on a platter. Drizzle lamb with tahini sauce or serve it on the side, for dipping. Sprinkle with parsley leaves, for garnish.