Adjust oven rack to lower-middle position and preheat oven to 375 degrees. Coat a roasting pan and rack with nonstick spray.
In a small bowl, mix together softened butter, garlic powder, 1 tablespoon salt and 1 1/2 teaspoons pepper. Set aside.
Starting at the back opening of the chicken, use your fingers to carefully separate the skin from the meat on the chicken breast and thighs. Be careful not to tear skin. Spread about 1/4 cup of the butter mixture between the skin and meat of the chicken.
In a medium bowl, add potatoes, carrots, garlic cloves, Italian seasoning, 1 teaspoon salt, and 1/2 teaspoon pepper. Drizzle with olive oil and toss to combine. Spread vegetables evenly in bottom of roasting pan.
Fold wings of chicken across back with tips touching. Tie drumsticks together with kitchen twine. Place chicken, breast side up, in the center rack and set in roasting pan. Brush chicken with remaining garlic-butter mixture.
Roast uncovered for 1 1/2 to 2 hours, until a thermometer inserted near the thigh reaches an internal temperature of 180 degrees. Rotate baking dish after 30 minutes.
Remove from oven and transfer chicken to a rimmed baking sheet. Tent with foil for 15 minutes before carving.
Meanwhile, return roasting pan to oven and continue to cook the vegetables until they are golden brown and fork tender, about 10 to 15 minutes longer. Remove vegetables with a slotted spoon and serve with roasted chicken.