Add broth, diced tomatoes, and chicken breasts and bring back to a simmer! If using already cooked leftover shredded chicken, don’t add it until the next step.
When chicken is cooked, carefully remove from the soup to a cutting board. Shred using two forks or cut into bite sized pieces and return it to the soup.
Turn off the heat. Add a few big handfuls of baby spinach and stir until wilted. Season to taste with salt and pepper.