Heat the olive oil in a 10-inch skillet over medium-high heat. Add the chicken, onion, bell pepper, mushrooms, and garlic. Sauté until the chicken is brown and the vegetables are tender, about 10 minutes.
Add the broth, tomatoes with juice, Italian seasoning, and salt and pepper to taste. If you want a thicker sauce, add optional cornstarch dissolved in 1 tablespoon water. Bring to a boil.
Reduce heat to low. Cover and simmer for 10 minutes. Add more salt and pepper to taste, if needed.
Top with the fresh parsley and Parmesan cheese, if using, and serve.
Notes
A cornstarch slurry can be added as a thickener if desired.Additional spices, such as thyme and rosemary, can be added.Capers, traditionally used in this dish, can also be added. Black pitted olives are another great addition.This dish goes well served over cauliflower rice or noodles.