In a large stockpot or Dutch oven, cook onions, sugar, salt, and pepper in olive oil over medium heat for about 25 minutes or until onions are tender and caramel colored, stirring occasionally.
Stir in chicken broth, undrained tomatoes, tomato sauce, oregano, garlic, and bay leaves. Bring to boiling. Add the orzo; reduce heat and simmer, covered, about 15 minutes or until pasta is tender; stir occasionally. Remove bay leaves.
Ladle soup into warm bowls. Top with croutons and Swiss or Parmesan cheese. Makes 8 side-dish servings.