01 - Lightly grease the slow cooker insert with nonstick spray or butter to prevent sticking.
02 - Arrange the cubed chicken breasts evenly across the bottom of the slow cooker. Sprinkle with salt, black pepper, and Italian seasoning to coat.
03 - Scatter the minced garlic over the seasoned chicken, then distribute the cubed cream cheese in small dollops across the top.
04 - Pour the heavy cream and basil pesto sauce over the chicken mixture. Stir gently to combine all ingredients without disturbing the chicken layer too much.
05 - Cover the slow cooker and cook on the low setting for 3 hours, allowing the chicken to become tender and the flavors to meld together.
06 - After 3 hours, stir in the cheese tortellini, halved cherry tomatoes (if using), and chopped baby spinach. Fold gently to incorporate without breaking the tortellini.
07 - Sprinkle the shredded mozzarella and grated Parmesan cheese evenly across the surface of the casserole.
08 - Cover and continue cooking on low for an additional 30 to 45 minutes, until the tortellini is cooked through and the cheese on top is fully melted and bubbly.
09 - Stir the casserole thoroughly before serving to distribute the melted cheese and sauce evenly. Taste and adjust seasoning if needed.