Whisk marinade ingredients:
Combine minced garlic, fresh lemon juice, olive oil, cumin, paprika, coriander, cinnamon, black pepper, and salt in a big bowl, whisking thoroughly.Dry and coat chicken:
Use paper towels to dry the chicken pieces thoroughly. Transfer the chicken to the bowl with the marinade and rub it in with your hands, ensuring every surface is evenly coated.Refrigerate marinated chicken:
Wrap the bowl with plastic film and refrigerate for a minimum of 2 hours, or up to 8 hours (overnight is fine).Arrange chicken on onions:
Preheat the oven to 425°F (220°C). Spread the thinly sliced onion over the base of a baking dish. Place the marinated chicken on top, skin side up, leaving space between pieces.Roast until golden:
Drizzle any leftover marinade from the bowl over the chicken. Roast for 35-40 minutes until the skin is golden and crisp, and the thickest part of the chicken reaches 165°F (75°C) internally.Rest and garnish:
Let the chicken rest for 5-10 minutes after removing from the oven. Sprinkle with chopped fresh parsley and offer lemon wedges for squeezing at the table.