Season chicken breasts with garlic powder, salt, and pepper.
Place seasoned chicken in slow cooker.
In a bowl, combine chicken broth, marinara sauce, and Italian seasoning.
Pour sauce mixture over chicken.
Cover and cook on LOW for 6 hours or HIGH for 3 hours.
In final 30 minutes, sprinkle with mozzarella and Parmesan.
Continue cooking until cheese is melted and bubbly.
Garnish with fresh basil before serving.