Season the chicken breasts with salt, black pepper, and dried Italian seasoning on both sides.
Heat olive oil in a skillet over medium heat and sauté the chopped onion and minced garlic until translucent and fragrant, about 3 minutes.
Place the seasoned chicken breasts in the bottom of the slow cooker.
Pour the sautéed onion and garlic over the chicken in the slow cooker.
Add the marinara sauce and water to the slow cooker, stirring gently to combine.
Cover and cook on low for 4 hours.
After 4 hours, remove the chicken breasts and shred them using two forks.
Return the shredded chicken to the slow cooker and stir to combine.
Add the uncooked ziti pasta to the slow cooker and stir to submerge the pasta in the sauce.
Cover and cook on low for an additional 30 minutes, or until the pasta is tender, stirring halfway through to prevent sticking.
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 on top, cover, and cook for 5 more minutes until the cheese melts.
Garnish with chopped fresh basil before serving.