In the crockpot, add the chicken breast, onions, celery, carrots, basil, Italian seasoning, garlic, and chicken broth. Season with salt and pepper.
Cover and cook on low for 6-8 hours or high for 4-6 hours.
After the 4 (or so) hours have elapsed, take two forks and shred chicken directly in the crockpot.
Add cornstarch and whisk to incorporate. Pour in heavy cream and add frozen gnocchi and spinach. Stir to combine and cover; cooking for additional 30 minutes on low.
Stir to combine and make sure that all the spinach is wilted and cooked before serving.