Add onion, garlic, mint, parsley and chilli flakes to food processor and pulse until finely chopped. Add lamb to a large mixing bowl and add onion mixture, cumin, allspice, salt and pepper. Gently mix with a wooden spoon or by hand until combined.
Form meat into small golfball sized balls and flatten slightly into hockey puck shape. Place on an oiled plate or platter and brush a teaspoon of oil across the tops of the kofta. Place in fridge for 10 minutes or more to allow the lamb to firm up which helps hold it's shape during grilling.
Prepare hummus sauce. Combine hummus and lemon juice in a small bowl and stir until consistency is a bit runny - add more lemon juice if needed. Set aside.
Heat a large heavy bottomed frying pan or skillet on medium-high heat. Add a teaspoon of oil to the pan. Place the kofta onto the grill and cook for 5 to 6 minutes, turning half way to brown both sides. Remove from heat and garnish with sesame seeds and sumac. Serve with fresh lemons wedges and hummus sauce.