Prepare the marinade by combining in a large bowl all the ingredients. Then add the chicken pieces and toss to incorporate. Cover with a plastic wrap and refrigerate for overnight or even better for 2 nights.
Remove from the refrigerator 1 hour prior to cooking and put on skewers loosely packed with layers of the onion and green pepper squares in-between every two pieces of chicken while discarding any excess marinade and the garlic.
Prepare your coals and once well rested and having created a nice grey ash, spread them all over the grill’s base.
Place your skewers on the grill and cook for about 10’, turning frequently and until chicken is cooked through and nicely charred. If using metal skewers, they help to cook the inside of the chicken cubes.
In the meantime, prepare the salad by adding in a plate the onions, parsley, pour the lemon juice, sprinkle the sumac, season with the salt and lightly toss.
Take off the grill and place on a plate where half the pitta bread is lined, garnish with sumac and cover with the rest of the pitta bread. Cover with foil for 5-10’ and then enjoy with the salad added to the side of the plate.