Heat oil in a large nonstick skillet over medium-high heat. Add onion and garlic to skillet and cook for 3 minutes or until softened. Add chicken to skillet and cook, stirring frequently, for about 4 minutes or until no longer pink. Add spinach, pesto, salt and pepper to skillet and stir until well blended; set aside.
In a small bowl, combine ricotta and 1/2 cup of the Italian shredded cheese.
Coat slow cooker bowl with nonstick cooking spray, then layer a third of the uncooked noodles, overlapping as necessary. Spread a third of the chicken mixture over noodles, then top with 1/4 cup water. Dollop a third of the ricotta mixture on top, and continue layering with remaining noodles, meat, an additional 1/4 cup water and ricotta mixture.
Cover and cook on HIGH for 3 hours or LOW for 5 1/2 hours. Sprinkle remaining 1/4 cup of Italian cheese on top for last 15 minutes of cook time or until melted.