01 - Lightly grease the inside of a 5-to-6-quart slow cooker with cooking spray or a thin coating of oil.
02 - Spread the cubed chicken breasts evenly across the bottom of the slow cooker. Season with salt and freshly ground black pepper.
03 - Scatter the finely chopped onion and minced garlic over the seasoned chicken.
04 - Layer the halved cherry tomatoes and roughly chopped baby spinach on top of the aromatics.
05 - In a mixing bowl, whisk together the heavy cream, low-sodium chicken broth, and basil pesto sauce until smooth and well combined.
06 - Pour the pesto cream mixture evenly over all the layered ingredients in the slow cooker.
07 - Sprinkle 1 cup of the shredded mozzarella and 1/4 cup of the grated Parmesan over the sauce. Stir gently just to combine, then cover with the lid.
08 - Cook on the LOW setting for 3 hours until the chicken is nearly cooked through and the flavors have melded.
09 - After 3 hours, gently fold in the refrigerated cheese tortellini. Re-cover and continue cooking on LOW for another 45 minutes to 1 hour, or until the tortellini are tender and the chicken is fully cooked.
10 - Top with the remaining mozzarella and Parmesan. Cover and let stand for 5 minutes until the cheese melts. Sprinkle with crushed red pepper flakes and fresh basil if desired before serving.