Mix the garlic, olive oil and lemon juice together in a reusable plastic container or bowl. Stir in all the spices, oregano, a large pinch of salt and the yogurt, then mix to make a paste. Tip in the chicken, tossing to coat, then cover and marinate for at least 1 hr, or chill overnight.
To make the dressing, mix all the ingredients together in a small bowl, season, cover and chill until needed. Can be made up to two days ahead. Toss all the salad ingredients, except the lemon juice and olive oil, together. The salad can be assembled 1-2 hrs ahead and kept chilled.
Light the barbecue or heat a griddle pan over a high heat. Cook the marinated chicken for 5 mins on each side, or until lightly charred and cooked through. Lift onto a board and set aside.
Drizzle the salad with the lemon juice and olive oil, then season with salt and toss everything together. Scatter the salad over a large platter or tip into a large serving bowl. Slice the chicken, then arrange it over the salad (or serve it on the side if you’re also cooking for vegetarians). Serve the salad with the tahini dressing on the side for drizzling over, along with toasted flatbreads or pittas for stuffing the chicken into and pickled chillies, if you like.
