01 - Lightly coat the inside of a 5 to 6 quart slow cooker with cooking spray or a thin layer of oil.
02 - Spread the cubed chicken breasts evenly across the bottom of the slow cooker and season with salt and black pepper.
03 - Scatter the finely chopped onion and minced garlic over the chicken, then layer the halved cherry tomatoes and chopped spinach on top.
04 - In a mixing bowl, whisk together the heavy cream, chicken broth, and basil pesto until smooth and well blended.
05 - Pour the pesto cream mixture evenly over the layered ingredients in the slow cooker.
06 - Sprinkle 1 cup of mozzarella and 1/4 cup of Parmesan over the sauce, then stir gently to combine all ingredients.
07 - Cover the slow cooker and cook on the LOW setting for 3 hours.
08 - After 3 hours, gently fold in the refrigerated cheese tortellini, re-cover, and continue cooking on LOW for another 45 minutes to 1 hour until the tortellini are tender and the chicken is cooked through.
09 - 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.