Mix the sumac, thyme and grated lemon rind with the olive oil. Season to taste, then rub all over the chicken and set aside for 5 minutes.
Heat a griddle pan until smoking hot. Cook the pitta breads for 1–2 minutes on each side until lightly browned, then set aside.
Cook the chicken thighs for 4–5 minutes on each side until lightly charred and cooked through. Squeeze a little lemon juice over the rocket and divide between serving plates. Cut the chicken into pieces and arrange on the plates with a spoonful of hummus and the pitta breads, torn into strips.