Place cumin,paprika,turmeric,caster sugar,olive oil,garlic and ginger in a large bowl and whisk to combine. Place chicken thighs in marinade and toss until coated. Place in fridge to marinate for at least 1 hour.
Preheat barbecue to hot. Scrape excess marinade from chicken and barbecue chicken for 7-8 minutes on each side or until cooked right through.
Meanwhile,toast buns,cut side down,on barbecue for about 1 minute.
To serve,place bun bottoms on serving plates. Top each with chilli relish (or serve it in a separate bowl),then add lettuce,coriander,onion and cucumber. Finish with a chicken thigh. Drizzle over a little tahini (or serve in a separate bowl),and top with bun tops. Serve immediately.
Tahini sauce
Place tahini,garlic,salt,oil,lemon juice and the warm water in a bowl and mix to combine.
Place in a serving bowl and sprinkle with parsley and sumac.
Chilli relish
Place all ingredients in a small saucepan over a medium-high heat.
Bring to the boil,then reduce heat to a gentle simmer and cook for 30 minutes.
Place in serving bowl and allow to cool before serving.