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