Make the shawarma marinade: in a mixing bowl combine lemon juice, olive oil, 6 cloves minced garlic, kosher salt, black pepper, ground cumin, paprika, turmeric, a pinch of cinnamon, and crushed red pepper flakes.
Add the chicken thighs to the marinade, toss to coat, cover, and refrigerate for at least 1 hour or overnight.
Cook the jasmine rice according to package instructions; keep warm.
Make the tzatziki: combine 1 cup plain Greek yogurt, 2 minced garlic cloves, the peeled and diced small cucumber, 1/2 teaspoon dried dill, 3 teaspoons fresh lemon juice, and salt and pepper to taste; stir until smooth and refrigerate until serving.
Preheat the oven to 425°F (220°C). Grease or line a baking pan.
Remove the marinated chicken from the fridge and place the thighs and the roughly chopped red onion on the prepared baking pan in a single layer, discarding excess marinade if desired.
Roast the chicken and onion for 30–40 minutes, until the internal temperature of the chicken reaches 165°F (74°C) and edges are golden; let the chicken rest a few minutes, then slice or chop.
Assemble the bowls: divide the cooked rice among bowls, top with sliced chicken and roasted onion, add scoops of hummus, chopped cucumber, and halved cherry tomatoes.
Finish each bowl with a dollop of tzatziki, chopped parsley, optional feta crumbles, and a sprinkle of crushed red pepper if desired.