Heat oven to 450º.
Rub outside of chicken with 1 tablespoon oil; season with a few pinches of salt.
Stuff cavity with rosemary and squeeze orange pieces to release juices.
Scatter vegetables in a roasting pan. Toss with remaining oil and a pinch of salt and pepper. Place chicken on top of vegetables breast side up.
Roast 30 minutes; then lower oven temperature to 350º and cook 30 to 45 minutes longer, or until a thermometer inserted into the thigh reads 165º.
Remove from oven and let rest 20 minutes before slicing. Serve with roasted vegetables and pan juices.