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 loosen the skin over the chicken breast areas using your fingers. Rub half of the marinade beneath the skin across the breast meat, ensuring even distribution.
03 - Rub the remaining marinade over the entire exterior surface of the chicken, coating evenly including legs, wings, and back.
04 - Place several lemon slices and some onion rings inside the chicken cavity to infuse interior moisture and flavor during roasting.
05 - Distribute 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 chicken to rest at room temperature for 30 minutes before cooking. For enhanced flavor, cover and refrigerate up to 8 hours, then bring to room temperature prior to roasting.
07 - Set oven to 400°F and allow to fully preheat before placing chicken inside.
08 - Position roasting pan on the middle rack. Roast 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 reads 165°F.
09 - Transfer 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.