Place chicken breasts or thighs at the bottom of the crockpot. Season with Italian seasoning, salt, and pepper. Sprinkle minced garlic on top.
Pour Alfredo sauce and chicken broth evenly over the chicken. Cover and cook on low for 4–5 hours or high for 2–3 hours, until chicken is tender and cooked through.
About 30 minutes before serving, use two forks to shred the chicken directly in the crockpot.
Stir in the cheese tortellini and spinach (if using). Mix gently to coat everything in the sauce.
Cover and cook for another 25–30 minutes on low, until the tortellini is tender but not overcooked.
Stir in shredded Parmesan until melted and creamy. Adjust seasoning to taste.
Spoon into bowls, garnish with chopped parsley, and serve warm.