01 - Whisk together olive oil, zaatar, sumac, lemon zest, lemon juice, minced garlic, kosher salt, and black pepper in a small mixing bowl until thoroughly combined.
02 - Gently lift the skin covering the chicken breast using your fingers. Rub half of the marinade directly under the skin, distributing evenly over the meat.
03 - Rub the remaining marinade over the entire exterior surface of the chicken, ensuring even coverage on all sides.
04 - Place a few lemon slices and some onion rings inside the chicken cavity to infuse additional flavor during roasting.
05 - Spread 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.
06 - Allow the chicken to rest at room temperature for 30 minutes before cooking. For deeper flavor penetration, refrigerate for up to 8 hours, then bring to room temperature prior to roasting.
07 - Set oven temperature to 400°F.
08 - 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 reads 165°F.
09 - Remove the chicken from the oven and let it rest for 10 minutes. This allows juices to redistribute throughout the meat. Carve and serve with roasted vegetables and pan juices.