Sauté chopped onion and garlic in hot olive oil in a large Dutch oven until tender. Add chicken broth and next 5 ingredients; bring mixture to a boil. Reduce heat, and simmer 10 minutes or until zucchini is tender.
Sprinkle 1/2 teaspoon Parmesan cheese on each baguette slice, and place on baking sheet. Broil 5 1/2 inches from heat (with electric oven door partially open) about 3 minutes or until cheese is melted.
Ladle soup into individual serving bowls; top each with a toast slice.