Season the chicken breasts with salt, black pepper, and dried Italian seasoning on both sides.
In a skillet, heat olive oil over medium heat. Add the chopped onion and minced garlic and sauté until softened, about 3 minutes.
Place the seasoned chicken breasts in the bottom of the slow cooker.
Pour the sautéed onion and garlic over the chicken.
Add the marinara sauce and water to the slow cooker, spreading evenly over the chicken.
Cover and cook on low for 3 hours.
After 3 hours, remove the chicken breasts from the slow cooker and shred them using two forks.
Return the shredded chicken to the slow cooker and stir to combine with the sauce.
Add the dry ziti pasta to the slow cooker and stir to submerge the pasta in the sauce.
Cover and cook on low for an additional 1 hour and 30 minutes, or until the pasta is tender.
Once the pasta is cooked, stir in the ricotta cheese, half of the shredded mozzarella, and half of the grated Parmesan cheese until well combined.
Sprinkle the remaining mozzarella and Parmesan cheese evenly over the top.
Cover and cook on low for 10 more minutes, or until the cheese is melted.
Garnish with chopped fresh basil before serving.