01 - Season the chicken breasts generously with salt and pepper on both sides, ensuring even coverage for maximum flavor penetration.
02 - Place the seasoned chicken breasts in a single layer at the bottom of the slow cooker.
03 - Combine crushed tomatoes, drained diced tomatoes, chopped onion, minced garlic, tomato paste, oregano, thyme, sugar, red pepper flakes, and olive oil in a large bowl. Mix thoroughly until all ingredients are well incorporated.
04 - Pour the tomato mixture evenly over the chicken, ensuring the breasts are completely covered by the sauce.
05 - Cover and cook on LOW setting for 6 hours or HIGH setting for 4 hours, until the chicken reaches an internal temperature of 165°F and is tender throughout.
06 - During the final 30 minutes of cooking, stir in the chopped fresh basil. If making a creamy version, add the heavy cream or half-and-half at this time and stir well to combine.
07 - Taste the sauce and adjust salt, pepper, or red pepper flakes as needed to suit your preference.
08 - Serve hot over rice, pasta, or with crusty bread. Garnish with additional fresh basil and grated Parmesan cheese if desired.