Preheat the oven to 325 degrees F (165 degrees C). Cover the hole of a fluted tube pan (such as Bundt(R)) with aluminum foil.
Pat chicken dry with a paper towel. Toss potatoes, carrots, and onion in a bowl with 2 tablespoons olive oil. Season with salt and pepper. Place vegetables in the bottom of the prepared pan.
Cut celery into 2 pieces. Place in the cavity of the chicken and set chicken upright over the aluminum-foil-covered center of the prepared pan. Rub remaining olive oil onto the chicken; sprinkle with salt, pepper, and onion powder.
Bake in the preheated oven until no longer pink at the bone and the juices run clear, about 50 minutes. An instant-read thermometer inserted into the thickest part of the thigh, near the bone, should read 165 degrees F (74 degrees C). Remove chicken from the oven and transfer to a plate. Cover with a doubled sheet of aluminum foil, and allow to rest in a warm area for 5 minutes before carving.