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Instructions
Combine olive oil, garlic, lemon juice, paprika, cumin, lemon zest, coriander, pepper flakes, salt, pepper, turmeric, and cinnamon in a 1-gallon resealable plastic bag. Seal the bag and gently squeeze until ingredients are well blended. Add chicken thighs, coat with marinade, squeeze out excess air, and seal the bag again. Marinate in the refrigerator for at least 2 hours or overnight.
Set a rack in the center of the oven and another about 6 inches from the broiler. Preheat the oven to 425 degrees F (220 degrees C). Lightly grease a 12x18-inch sheet pan.
Spread onion slices onto the prepared sheet pan, then place marinated chicken thighs on top; keep as much marinade on each thigh as possible. Discard any remaining marinade.
Bake on the center rack of the preheated oven until no longer pink at the bone and the juices run clear, about 30 minutes. An instant-read thermometer inserted near the bone should read 165 degrees F (74 degrees C). Turn on the broiler and move the sheet pan to the upper rack. Broil until a light char develops, 2 to 3 minutes. Garnish with parsley.