Season the chicken breasts or thighs on both sides with salt, black pepper, and Italian seasoning.
Arrange the seasoned chicken in the bottom of the slow cooker.
Add the minced garlic, chicken broth, and heavy cream. Stir the liquid gently around the chicken to combine.
Cover and cook on LOW for about 4 hours or HIGH for about 2 hours, until the chicken is tender and has reached a safe internal temperature of 165°F (74°C).
Shred the chicken directly in the slow cooker using two forks, or remove it first if you prefer larger pieces.
Stir in the grated Parmesan cheese until melted and the sauce becomes creamy.
Let the Slow Cooker Garlic Parmesan Chicken rest for a few minutes so the sauce can settle and thicken slightly.
Garnish with fresh parsley, if desired, and serve warm.
Notes
Chicken breasts can be replaced with boneless, skinless chicken thighs for a richer result. For a slightly lighter sauce, replace part of the heavy cream with additional chicken broth, although the finished sauce will be thinner.