Heat oil in nonstick Dutch oven or large saucepan over medium heat until hot. Add onions; cook 15 to 20 minutes or until tender and brown, stirring occasionally.
Stir in broth and pepper. Bring to a boil. Reduce heat to low; simmer 10 minutes.
Meanwhile, place bread slices on ungreased cookie sheet. Broil 4 to 6 inches from heat for 45 to 60 seconds or until lightly toasted. Turn slices over; top untoasted sides with Swiss cheese. Sprinkle with Parmesan cheese. Broil 30 to 45 seconds or until cheese is melted.
To serve, ladle soup into 4 individual soup bowls; top with cheese toast. Spoon small amount of broth over top.