In a medium glass bowl, whisk together all the spices, oil, lemon juice, and greek yogurt. Toss in the chicken thighs. Cover and marinate in the fridge for at least an hour but, optimally, overnight.
Preheat the oven to 425° F.
Add onion and garlic to the bowl and toss in to soak up a little of the marinade.
Use a cast iron skillet or enamel baking dish for the best results. Pour the contents of your bowl, leftover marinade and all, into the baking dish. Bake for 40 to 45 minutes until golden brown and a little crispy around the edges.
Let the chicken rest for 5 minutes for the juices to set before slicing.
For the garlic sauce, throw everything in a blender and let it go for 2 minutes.
You'll have enough sauce for leftovers, sandwiches, etc. Keep it in the fridge.
To build a wrap, start by lightly warming a pita on both sides over low heat on the stove. Spread a little hummus to start (you could also forgo the hummus and add tahini to the top). Pile on as much shawarma as you like, and then add pickled turnips, and sliced tomato and cucumber. Drizzle with garlic sauce, and enjoy.