Use paper towels to pat the chicken dry, then season with salt and pepper. In a large Dutch oven over medium-high, heat 1 tablespoon of the oil until just smoking.

Add half of the chicken in a single layer and cook until well browned, 5 to 7 minutes. Transfer to a bowl. Repeat with another tablespoon of oil and the remaining chicken. Set the chicken aside.

Chop ¼ cup of the pine nuts and set aside. With the pot over medium, heat 2 tablespoons of the remaining oil. Add the onion and cook, stirring, until softened slightly, about 5 minutes.

Add the garlic, chopped pine nuts, 3 tablespoons of the sumac and paprika. Cook, stirring, until fragrant, 30 to 60 seconds. Add the water, stir to combine and bring to a simmer.

Return the chicken and any juices to the pot. Cover, reduce the heat to medium-low, and simmer until tender, 25 to 30 minutes.

Heat the oven to 450ºF with a rack in the middle position. Use a slotted spoon to transfer the chicken to a bowl. Use 2 forks to shred the meat into bite-size pieces.

Bring the liquid in the pot to a simmer over medium-high. Cook, stirring, until most of the moisture has evaporated, 10 to 15 minutes. Return the chicken to the pot and stir in the remaining ¼ cup whole pine nuts. Taste and season with salt and pepper. Cover and set aside.

Brush the pita on both sides with the remaining 2 tablespoons oil and arrange the rounds on a rimmed baking sheet. Bake until heated through and softened, 5 to 7 minutes.

Sprinkle with the remaining 1 tablespoon sumac, then cut each round in half and transfer to a platter. Stir the parsley into the chicken and transfer to a serving bowl. Serve the chicken with the pita and tahini for drizzling.