01 - Rub both sides of each chicken breast with salt and black pepper, ensuring even coverage.
02 - Place seasoned chicken breasts in a single layer at the bottom of the slow cooker.
03 - In a large bowl, combine crushed tomatoes, diced tomatoes, onion, garlic, tomato paste, oregano, thyme, sugar, red pepper flakes if using, and olive oil. Mix thoroughly until uniform.
04 - Evenly distribute the tomato mixture over the chicken breasts in the slow cooker.
05 - Cover and cook on LOW setting for 6 hours or HIGH for 4 hours, until chicken reaches internal temperature of 165°F and is tender.
06 - During the final 30 minutes of cooking, stir in chopped fresh basil and heavy cream if making a creamy version.
07 - Taste sauce and add additional salt or pepper if desired.
08 - Plate hot chicken with sauce, garnish with extra fresh basil and Parmesan cheese. Accompany with rice, pasta, or crusty bread.