Add chicken breasts, marinara sauce, onion powder, Italian seasoning, minced garlic, salt, and black pepper to the crockpot
Cook on low until chicken is tender and cooked through
Shred the cooked chicken and mix with the marinara sauce
Toast sub rolls and brush with melted butter
Fill each sub roll with the marinara chicken mixture
Top with provolone cheese, mozzarella cheese, and Parmesan cheese
Garnish with chopped fresh parsley and serve
