In a large stockpot, boil chicken for about 20 minutes. Drain and remove chicken from pot to shred.  Set aside.

Dice onion, slice carrots, chop celery, mince garlic. Heat olive oil in the same large stockpot over medium heat. Add the onions, carrots, celery, and garlic.  Return chicken to pot and add pepper, salt, thyme, chicken broth, gnocchi, and spinach.  Cook until bubbly, then turn down to simmer. Simmer for 15 more minutes.  

Whisk cold milk and cornstarch together.  Pour into soup and allow to simmer for 10 more minutes.

Top with spinach and grated parmesan cheese.