To make the marinade; stir together 1 cup yoghurt, lemon juice, chilli sauce and vinegar. Stir in the garlic, onion, pepper, chilli flakes, mace and salt. Marinate the chicken overnight in the refrigerator.
Place oven rack in the top position and turn oven on to grill.
To cook; drain the marinade from the meat and place on a slotted grill pan. Grill on top rack of preheated oven turning after a few minutes until cooked through; about 5 minutes.
To assemble the kebab; spread each pita with a tablespoon of plain yoghurt and layer with onion, tomato and cucumber. Pile on the chicken and dress with Ranch dressing.