Fill wishbone area of chicken with stuffing. Fasten neck skin to back with skewer. Fold wings across back with tips touching. Fill body cavity lightly. (Do not overstuff) The stuffing will expand while cooking. Place chicken, breast side up, in shallow roasting pan. Cut onions in half and arrange around the chicken. Brush chicken and onions with margarine. Roast uncovered in 375 F oven, brushing chicken and onions several times with remaining margarine until chicken and onions are done, about 1 1/2 hours. Oat Stuffing Cook and stir onion in margarine in 10 inch skillet over medium heat unitl light brown. Stir in remaining ingredients. Cook and stir until oats are golden brown and crip, about 3 to 4 minutes.