01 - Whisk together olive oil, zaatar, sumac, lemon zest, lemon juice, garlic, salt, and pepper in a small bowl until well combined.
02 - Gently loosen the skin over the chicken breasts. Rub half the marinade under the skin, then coat the entire exterior with the remaining mixture.
03 - Place lemon slices and onion rings inside the chicken cavity for added moisture and flavor.
04 - Spread remaining onion rings, carrot chunks, and lemon slices in the roasting pan. Position the chicken breast side up on top of the vegetables.
05 - Let chicken stand at room temperature for 30 minutes, or refrigerate covered for up to 8 hours for deeper flavor penetration. Bring to room temperature before roasting.
06 - Set oven to 400°F for optimal roasting temperature.
07 - Roast in the center of the oven for 1 hour to 1 hour 15 minutes, until juices run clear and an instant-read thermometer inserted into the thickest thigh meat reads 165°F.
08 - Allow chicken to rest for 10 minutes before carving to redistribute juices. Serve with roasted vegetables and pan juices.