Preheat your oven to 425 degrees.
Mix together the salt, garlic powder, onion powder, and pepper in a small bowl. Reserve 1/2 tablespoon of the mixture.
In a small bowl, combine the room temperature butter, the remainder of the spice mix, and the remaining 3 cloves of minced garlic.
Spread the butter mixture underneath the chicken's skin.
In the base of a roasting pan toss the carrots, potatoes, and onion with the 1/2 tablespoon reserved spice mix, 3 crushed garlic cloves, 2 springs of fresh thyme and 1 tablespoon of oil.
Place the remaining thyme in the chicken, and both lemon halves. Tie the legs of the chicken together with kitchen string and tuck the wing tips under the chicken. Place the chicken on top of the vegetables and brush with the remaining olive oil.
Roast the chicken and vegetables for 1 1/2 hours or until the juices run clear when cut between the body of the chicken and thigh. (Chicken should reach an internal temperature of 165 degrees.) Remove the chicken and tent with aluminum foil for 20 minutes before serving.