Preheat the oven to 350 degrees F with a rack in the middle.
Then put the chicken breast side up on a roasting rack in a roasting pan.
Stuff chicken with the lemon garlic, onion and rosemary sprigs.
In a small bowl, whisk together horseradish, honey, olive oil, salt and pepper.
Spread all over the chicken, making sure to get under the skin as well.
Truss the chicken, or tuck the wings under the body and tie together the legs.
Roast chicken for 1 hour and 20 minutes, and then turn the oven up to 450 degrees F to brown the skin. Continue cooking about 20 more minutes until the internal temperature near the thighbone is 160 degrees F and the juices run clear (it should continue to cook once removed from the oven until the temperature is 165 degrees F).
Let chicken rest for 20 minutes covered with aluminum foil before carving. Garnish with parsley if desired.