In a small bowl, mix Italian seasoning, garlic powder, salt, and black pepper. Rub the seasoning mixture evenly over the chicken breasts.
Heat olive oil in a skillet over medium heat. Add chopped onion and minced garlic and sauté for 3-4 minutes until softened and fragrant.
Place the seasoned chicken breasts in the bottom of the slow cooker. Pour the sautéed onion and garlic over the chicken.
Pour marinara sauce and water over the chicken and onions in the slow cooker.
Cover and cook on low for 4 hours, until the chicken is cooked through and tender.
Remove the chicken breasts from the slow cooker and shred them using two forks.
Add the dry ziti pasta to the slow cooker and stir to combine with the sauce.
Return the shredded chicken to the slow cooker and stir well to combine all ingredients.
Cover and cook on high for 30 minutes, stirring halfway through, until the pasta is tender.
Turn off the slow cooker. Stir in ricotta cheese, half of the mozzarella cheese, and half of the Parmesan cheese until well combined.
Sprinkle the remaining mozzarella and Parmesan cheese evenly over the top. Cover and let sit for 5 minutes to allow the cheese to melt.
Garnish with chopped fresh basil before serving.