Pre-heat barbecue for indirect heat to 350°F, either mounding charcoal on one side of bbq only, or turning off one section of gas burners.
Chop bread into cubes and place in a large bowl.
Add the poultry spice, salt and pepper, and Worchestershire sauce and stir.
Sauté chopped onion in olive oil just until the onions turn translucent and soften. Then pour the onions and olive oil into the bowl of bread cubes and stir.
Add melted margarine (or butter) and stir.
Cut top 1/4 from large onions and using a grapefruit spoon hollow out the onions so there is a nice sized hole in each one. I suggest leaving 2-3 layers of onion on the outside.
Place each onion on a 12x12-inch square of aluminum foil, top with a pat of butter, and seal in foil.
Place foiled onions on the indirect (unheated side or portion) of the barbecue and cook at 350°F for 1 hour.
Carefully remove foil and serve.