In a large 12-inch skillet, heat 1 tablespoon olive oil over medium high heat. Add the chicken in one layer, taking care not to overlap the pieces. Sprinkle with the Italian seasoning and ½ teaspoon salt.
Cook the chicken undisturbed, until golden brown on one side, about 5 minutes. Flip, and cook an additional 3 minutes until browned on both sides and just cooked through. Remove from the pan and set aside.
In the same pan, heat the remaining 1 tablespoon olive oil over medium heat. Add the zucchini, sprinkle with ½ teaspoon salt, and cook until just tender, stirring occasionally, about 5 minutes.
Add the garlic, and cook until fragrant, about 1 minutes, stirring occasionally.
Add chicken stock, stirring to deglaze, then add tomato paste and diced tomatoes, stirring until well combined.
Add the cooked chicken back to the pan, turn the heat to medium low, and simmer uncovered for 5 minutes, until the sauce is slightly reduced.
Turn off the heat, add the butter, and stir to combine. Taste the sauce and add additional salt if desired. Serve sprinkled with basil and red pepper flakes to taste.