01 - Pat the chicken breasts dry and season both sides generously with salt and freshly ground black pepper.
02 - Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Add the chicken breasts and sear for 3 to 4 minutes per side until deeply golden. Remove and set aside on a plate.
03 - In the same skillet, add 1 tablespoon of olive oil. Sauté the finely chopped onion for 2 to 3 minutes until softened and translucent. Add the minced garlic and cook for 30 seconds until fragrant.
04 - Pour in the crushed tomatoes along with the diced fresh tomatoes, dried oregano, chili flakes if using, and sugar. Stir well to combine and let the sauce simmer for 5 minutes to develop flavor.
05 - Return the seared chicken breasts to the skillet, nestling them into the sauce. Cover with a lid, reduce the heat to low, and simmer for 15 to 20 minutes until the chicken is cooked through and reaches an internal temperature of 165°F.
06 - Stir the torn basil leaves into the sauce and let everything simmer together for 2 more minutes to release the aroma.
07 - Serve hot, garnished with grated Parmesan cheese and additional fresh basil leaves. Pair with gluten-free pasta, rice, or roasted vegetables.