Soak 8 wooden skewers in cold water for 30 minutes.
To make the zathar spice mix, put the sesame seeds into a dry frying pan and toast over medium heat until golden and aromatic. Remove, let cool then transfer to a spice grinder (or clean coffee grinder). Add the thyme and salt and then blend to a coarse powder. Alternatively, use a mortar and pestle. You will need 3 tablespoons for this recipe (put the remainder into an airtight container and keep in a cool place for future use).
Put the 3 tablespoons of zathar spice mix and olive oil into a shallow dish and mix well. Cut the chicken into bite-sized pieces, add to the Zathar oil and toss well until coated. Let marinate in the refrigerator for at least 2 hours.
Preheat the barbecue, then thread the chicken pieces onto the soaked wooden skewers and cook over hot coal for 2-3 minutes on each side. Remove from heat, let rest briefly, sprinkle with chilli oil and lemon juice and serve hot with salad or pita bread.