In the slow cooker, pour in the tomato sauce and add the minced garlic, kosher salt, dried thyme, and freshly ground black pepper. Stir the ingredients together until well combined.

In a separate bowl, combine the heavy cream and cornstarch, whisking until the mixture is smooth and lump-free. Pour the cream mixture into the slow cooker, mixing gently.

Place the chicken breasts or thighs into the creamy sauce in the slow cooker, ensuring each piece is well-coated.

Cover the slow cooker and set it to low heat for 3 to 4 hours, allowing the chicken to become tender and the sauce to thicken.

Once the chicken is fully cooked, remove it from the slow cooker. Stir in the sun-dried tomatoes, Parmesan cheese, and a pinch of sugar into the sauce, followed by the baby spinach.

Serve the chicken with the sauce generously spooned over it, offering a comforting meal.