Slice the onion and break apart the pieces.Spray a frying pan with I Can’t Believe It’s Not Butter Spray and add the onion. Cook on medium-low for about 20 minutes – until they’re golden brown, stirring frequently.Add Worcestershire sauce to the ground sirloin and form a patty. Sprinkle the patty with garlic powder, salt and pepper.Cook the patty in a frying pan. I cooked mine 5 minutes on each side to get it medium-well.Remove patty from the pan and cover with foil.Spray one side of each slice of bread with I Can’t Believe It’s Not Butter Spray. To the other side add the slice of cheese, hamburger patty and sauteed onions.Cook in a clean frying pan for 2-3 minutes on each side, or until the bread is golden brown.