The size of the burgers can be whatever you’d like; just be sure to flatten them out as much as possible when shaping, so that they don’t get too thick and puck-ish when they cook. The raw meat mixture becomes quite soft with all of the seasonings and onion, so it’s helpful to chill it for a half hour or up to a day before grilling. Dress the burgers with toum garlic sauce, or standard mustard and ketchup. A quickie garlic sauce is mayonnaise with some minced garlic stirred in.
Combine the lamb with the onion, parsley, mint, salt, pepper, sumac, and cinnamon. Shape into 4-6 flat patties. Dip your hands in cold water if they become sticky, and to help smooth the meat into the patty. Place the patties onto a wax paper lined plate and chill for ½ hour or up to one day, covered.
Heat the grill to medium high heat. Brush the patties with olive oil. Grill about 4 minutes per side, or until cooked through. Serve on buns with condiments.