Line a 20cm (8-inch) spring-form pan with parchment paper. Put the bulgur in a bowl, add 200 milliliters (1 cup) of tap water and set aside for 30 minutes.
Place four tablespoons of oil in a large frying pan and saute the garlic, onion and chilli on medium-high heat until soft. Place in a bowl and set aside. Cook the lamb on high heat and cook until brown. Add the onion mixture back to the pan and add the spices, coriander, salt, pepper, and most the pine nuts and parsley. Cook for a couple of minutes and remove from the heat. Taste and adjust the seasonings, if necessary. You want the spiciness to come through the lamb.
Check if the water has been absorbed by the bulgar, if not, then strain it through a fine sieve and place back in the bowl. Add the flour, a tablespoon of oil, a quarter-teaspoon of salt, and a pinch of black pepper. Work into a pliable mixture, with your hands, until it just holds together. Push the bulgar mixture firmly into the base of the spring-form pan until it is compacted and level. Spread the lamb mixture evenly on the top and press down. Bake for 20 minutes.
In a medium bowl, whisk together the tahini, lemon juice, 50ml (3 tablespoons) of water and a pinch of salt. The sauce should be thick, yet pourable. Spread the sauce on top of the kubbeh, sprinkle on the remaining parsley and pine nuts and bake for 10 minutes until the tahini is set and the pine nuts are golden.
Before serving, sprinkle the sumac and drizzle a little olive oil on top. Cut into wedges.