Add in zucchini and red bell pepper, cooking for another 2 minutes until they begin to soften.
Sprinkle flour over the vegetables, stirring to form a roux, and cook for 1 minute. Gradually pour in chicken broth, stirring continuously until the mixture thickens.
Add Italian seasoning, optional red pepper flakes, beans, and diced tomatoes to the pot. Stir well to combine.
Bring the stew to a boil, then lower the heat and simmer uncovered for 25-30 minutes, stirring frequently.
Mix in the chopped chicken, spinach, and cider vinegar. Cook for an additional 3-4 minutes until everything is heated through.
Season with salt and pepper to taste. Serve hot, garnished with fresh parsley and Parmesan cheese if desired.