Preheat the oven to 375°F (190°C) and position a rack in the center.
In a small bowl, combine the salt, pepper, garlic powder, onion powder, Italian herbs, and 1/2 tablespoon poultry seasoning to make the seasoning blend; set aside.
Place the carrots, quartered onion, and halved potatoes in a bowl; toss with 1/2 tablespoon olive oil and about half of the seasoning blend until evenly coated, then spread them in an even layer in a rimmed baking pan.
Remove any giblets from the chicken cavity if present and pat the chicken dry with paper towels.
Rub 1 tablespoon olive oil all over the chicken. Mix the remaining 2 tablespoons poultry seasoning with any leftover seasoning blend and generously rub it over the chicken skin, inside the cavity, and into crevices.
Optionally place half a lemon inside the chicken cavity.
Place a wire rack over the vegetables if using, then set the chicken on the rack (or set the chicken directly on the vegetables if not using a rack).
Roast the chicken in the preheated oven until the internal temperature in the thickest part of the thigh reaches 165°F (about 90 minutes for a typical whole chicken); juices should run clear and there should be no pink near the bone.
When the chicken is done, remove it from the oven. Set the oven to broil on high.
Brush 1 tablespoon of butter over the top of the chicken and broil 2–3 minutes, watching carefully, until the skin is golden and crisp.
Remove the chicken from the oven and let it rest for at least 20 minutes to allow juices to settle before carving.
Carve the chicken, sprinkle with chopped cilantro, and serve with the roasted vegetables.