In the crockpot, add the chicken breasts, chopped onion, minced garlic, diced tomatoes, chicken broth, Italian seasoning, salt, and black pepper. Stir to combine.
Cover and cook on low for 6 hours or on high for 3 hours, until the chicken is cooked through and tender.
Once the chicken is fully cooked, use two forks to shred the chicken directly in the crockpot.
Add the frozen cheese tortellini and heavy cream to the crockpot. Stir gently to combine.
Cover and continue to cook on high for an additional 30 minutes, or until the tortellini is cooked through.
Stir in the chopped spinach and let it wilt for about 5 minutes before serving.
Taste and adjust seasoning if necessary.
Notes
Serve warm with grated Parmesan and fresh basil for garnish.