Season chicken breasts with salt, pepper, garlic powder, and Italian seasoning, then place them in the slow cooker.
Pour chicken broth around the chicken, sprinkle minced garlic and grated Parmesan over the top, and add butter pieces.
Cover and cook on low for 6 to 7 hours or high for 3 to 4 hours, until chicken is tender and easily shredded.
Remove chicken from slow cooker and shred with two forks.
Return shredded chicken to the slow cooker juices and stir to coat.
Assemble sandwiches by piling Parmesan garlic chicken onto rolls and adding optional toppings as desired.
Serve sandwiches warm with your favorite sides, such as chips, salad, or pickles.