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 over the chicken breast sections and rub half of the marinade directly underneath the skin, ensuring even coverage.
03 - Rub the remaining marinade over the entire surface of the chicken, pressing gently to adhere the spice blend.
04 - Place a few lemon slices and onion rings inside the chicken cavity for additional aromatic flavor during roasting.
05 - Spread the remaining onion rings, carrot chunks, and lemon slices evenly across the bottom of a roasting pan.
06 - Set the prepared chicken breast-side up on top of the vegetable bed in the roasting pan.
07 - Let the 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 if refrigerated.
08 - Set the oven to 400°F and allow it to fully preheat before inserting the chicken.
09 - Place the roasting pan in the center of the oven and cook for 1 hour to 1 hour 15 minutes, until the juices run clear and an instant-read thermometer inserted into the thickest part of the thigh reaches 165°F.
10 - Transfer the chicken to a cutting board and let rest for 10 minutes to allow juices to redistribute throughout the meat.
11 - Carve the chicken and serve with the roasted vegetables and pan juices spooned over the top.