Place the chicken breasts in the bottom of a crockpot. Season them with the salt, pepper, Italian seasoning, minced garlic and onion.
Pour the marinara sauce on top of the chicken.
Cook on low for 5 - 7 hours or on high for 2 1/2 - 3 hours until the chicken is cooked through (internal temperature of 165 degrees F).
Stir in the sliced zucchini. Cover and cook on high for 60 minutes until the zucchini is tender.
Top the meal with the shredded parmesan cheese. Cover and cook on low until the cheese is melted.
Then the chicken is ready to serve and enjoy.