01 - Whisk together olive oil, zaatar, sumac, lemon zest, lemon juice, minced garlic, kosher salt, and black pepper in a small bowl until thoroughly combined.
02 - Gently lift the skin covering the chicken breast area. Rub half of the prepared marinade beneath the skin, ensuring even distribution over the meat.
03 - Rub the remaining marinade over the entire exterior surface of the chicken, pressing gently to adhere the spice mixture to the skin.
04 - Place lemon slices and onion rings inside the chicken cavity to infuse additional moisture and flavor during roasting.
05 - Spread remaining onion rings, carrot chunks, and lemon slices across the bottom of a roasting pan. Position the chicken on top, breast side facing upward.
06 - Allow the chicken to rest at room temperature for 30 minutes. Alternatively, cover and refrigerate for up to 8 hours, then bring to room temperature before roasting for enhanced flavor penetration.
07 - Preheat oven to 400°F.
08 - 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 portion of the thigh reaches 165°F.
09 - Transfer the chicken to a cutting board and let rest for 10 minutes to allow juices to redistribute throughout the meat. Carve and serve with roasted vegetables and pan juices.