Chicken and Escarole Soup with Fennel

Heat oil in large pot over medium-high heat. Add chicken; sprinkle with salt, pepper, and oregano. Mix in onions, celery, garlic, and fennel seeds. Sauté until vegetables begin to soften, about 4 minutes. Stir in tomatoes. Add broth; bring to boil. Reduce heat to medium; simmer until vegetables and chicken are tender, about 15 minutes. Add escarole; simmer until wilted, about 3 minutes. Season with salt and pepper. Ladle into bowls. Serve, passing cheese separately.