Cook and stir onions in vegetable oil in a covered large saucepan over medium heat for 20 minutes. Stir in the beef broth, Worcestershire sauce and black pepper; heat to a boil.
Remove from heat.
Place bread on a baking sheet; sprinkle bread with cheese. Broil 4-to-5 inches from heat for about 1 minute or until cheese is melted and golden.