Place the meat in a large bowl and add the onion, celery, ketchup, horseradish, Worcestershire sauce and parsley. Season with salt and pepper. Mix well but do not overwork, then chill for 1 hour.
Divide the mix into 4 evenly sized burgers and brush liberally with oil.
Heat a chargrill or pan grill until hot, add the burgers and cook for 5-6 minutes.</