01 - Combine olive oil, zaatar, sumac, lemon zest, lemon juice, minced garlic, kosher salt, and black pepper in a small bowl. Whisk thoroughly until fully incorporated into a smooth paste.
02 - Carefully lift the skin covering the breast area and rub half of the marinade directly underneath. Massage the remaining marinade evenly over the entire exterior surface of the chicken.
03 - Place several lemon slices and onion rings inside the chicken cavity for enhanced moisture and flavor during roasting.
04 - Distribute the remaining onion rings, carrot chunks, and lemon slices across the bottom of a roasting pan. Position the chicken on top, breast side facing upward.
05 - Allow the chicken to rest at room temperature for 30 minutes before cooking. For deeper flavor penetration, cover and refrigerate for up to 8 hours, bringing to room temperature prior to roasting.
06 - Heat oven to 400°F.
07 - Place the roasting pan in the center of the oven. Cook for 1 hour to 1 hour 15 minutes until juices run clear and an instant-read thermometer inserted into the thickest part of the thigh reaches 165°F.
08 - Remove from oven and let the chicken rest for 10 minutes before carving. Serve accompanied by roasted vegetables and pan juices.