Place the chicken breasts, pesto, and chicken broth into your slow cooker. Give it a quick stir to combine.
Cover and cook on low for 6–7 hours or high for 3–4 hours, until the chicken is fully cooked and tender.
Remove the chicken from the slow cooker and shred it using two forks. Return the shredded chicken back into the soup.
Stir in the uncooked short pasta (like rotini or penne). Cover and cook on high for 20–25 minutes, or until the pasta is tender.
Once the pasta is cooked, stir in the spinach and salt. Let it sit for another 5–10 minutes until the spinach wilts.
Taste and adjust seasoning if needed, then serve warm. Enjoy your creamy, cozy slow cooker chicken pesto soup!