Marinate the chicken: Combine the lemon juice, olive oil, salt, cumin, paprika, turmeric, cinnamon and red pepper flakes in a large bowl, and whisk to combine. Add the chicken and toss well to coat. Cover and store in refrigerator for at least 30 minutes and up to 12 hours.
Preheat the oven to 400 degrees F.
Remove the chicken from the marinade, shaking off the excess and transfer to a plate.
To the bowl with the remaining marinade, add the zucchini, rice, chicken stock, and half the parsley or mint. Fold the ingredients together until well-mixed. Transfer to a 15-inch oven-proof skillet or a 9 x 13 casserole dish and arrange in an even layer. Nestle the chicken thighs in the rice mixture.
Bake the casserole for 45 minutes, or until the rice is tender and most of the liquid is absorbed. Remove from the oven and allow to rest for 5 minutes.
Meanwhile, prep the topping: Toss the cucumbers and tomatoes with olive oil and salt (and a splash of lemon juice, if desired). Scatter the vegetables on top of the casserole.
Optional: if you prefer the appearance of shawarma, you can remove the chicken thighs and thinly slice them, then return to the pan.
Scatter the cucumber-tomato topping over the casserole and serve alongside white sauce (see note) and hot sauce.