Grilled Chicken Shawarma with Charred Red Onion, Naan, and Tahini, Charred Red Onion, Naan, and Tahini

naan bread (enriched wheat flour (wheat flour, niacin, reduced iron, ascorbic acid as dough conditioner, thiamine mononitrate, riboflavin, enzyme, folic acid, buttermilk (skim milk, dry buttermilk, bacterial culture, water, soybean and/or canola oil, cultured wheat flour, sugar, baking powder (sodium acid pyrophosphate, sodium bicarbonate, cornstarch, monocalcium phosphate, sea salt, ghee, wheat gluten, dextrose, dextrin, vegetable fiber, yeast, persian cucumber, red onion, lemon, tahini paste, garlic, turmeric saffron powder, parsley, cayenne pepper