01 - Pat chicken breasts dry with paper towels and season generously with salt and black pepper on both sides.
02 - Heat olive oil in a large skillet over medium-high heat. Add chicken and sear for 3 to 4 minutes per side until a golden crust forms. Remove chicken and set aside on a plate.
03 - Reduce heat to medium. In the same skillet, add onion and sauté until translucent, about 3 minutes. Stir in garlic and cook until fragrant, about 30 seconds more.
04 - Add crushed tomatoes, fresh diced tomatoes, dried oregano, and red pepper flakes to the skillet. Stir to combine and simmer for 5 minutes, stirring occasionally.
05 - Return chicken breasts to the skillet, nestling them into the sauce. Cover with a lid and simmer for 15 to 18 minutes, or until chicken is cooked through and reaches an internal temperature of 165°F.
06 - Uncover the skillet and sprinkle chicken with Parmesan cheese. Let cook uncovered for 2 minutes until the cheese melts and the sauce thickens slightly.
07 - Scatter torn fresh basil over the top. Serve hot, spooning extra sauce over each chicken breast, with additional Parmesan as desired.