For the marinade: In a medium to large bowl, combine lemon juice, 1/2 cup olive oil, garlic, salt, pepper, cumin, paprika, turmeric, cinnamon and red pepper flakes. Whisk to combine.
Add chicken thighs and toss to coat them with the marinade. Cover and store in refrigerator for 1 hour up to 12 hours.
When ready to cook, preheat over to 425o F. Spray rimmed baking sheet with cooking spray or oil. Quarter the onions (or cut in large chunks) and coat with the marinade in the bowl. Remove the chicken and onion and place on baking sheet. Pour any remaining marinade over the chicken.
Roast the chicken in the oven until it is browned, about 30-40 minutes. Remove from oven and let sit a couple of minutes while you make the accompaniments if using. Serve and enjoy!