Mix the Spice Blend with the salt in a small bowl. Rub the chicken thighs all over with the mixture and roll up. Place each seasoned and rolled thigh on a piece of plastic wrap and tightly roll each in the plastic, securing the wrap under the rolls. Refrigerate for at least 2 hours or up to 2 days.
Bring a medium pot of water to a simmer. Carefully lower the wrapped chicken rolls into the hot water and poach them for 15 minutes. Transfer to an ice bath, then drain and refrigerate for at least 2 hours or up to overnight.
When you’re ready to serve the shawarma, unwrap the chicken and slice each roll thinly. Place a cast-iron skillet over medium-high heat and add the oil. Cook the sliced chicken, turning occasionally, for about 3 minutes, or until the pieces are slightly charred.