Heat the oven. Heat the oven to 400 degrees F and line a baking sheet with parchment.
Season and roast. Rub the slabs with olive oil, sprinkle both sides with the spice rub, and bake for 45 to 50 minutes until soft, without flipping.
Make the sauce. Whisk the yogurt, tahini, lemon juice, grated garlic, and salt in a heat proof bowl, microwave for 20 seconds, and whisk until creamy.
Toast and cook the topping. Toast the pine nuts in a dry pan and set aside. Heat the olive oil in the same pan and cook the garlic, shallot, and chilies until the garlic is golden, then move to a bowl.
Assemble. Spread most of the sauce on a plate, set a slab on top, and spoon over the topping.
Finish. Drizzle with more sauce, top with sesame seeds, pine nuts, cilantro, and sumac, and serve with toasted pita.