In a large bowl, add diced onions, minced garlic, breadcrumbs, cinnamon, oregano, parsley, rosemary, cumin, allspice, paprika, salt, pepper, and crumbled feta. Mix well, then crack in one egg and add ground lamb. Using clean hands or a spatula, combine until it comes together. Use a medium size ice cream scoop and then roll the lamb meatballs to almost 3" in size, as they will shrink on the grill.