Add in the mushroom slices and cook until all the liquid is evaporated (about 8 minutes).
Add in the onions, garlic, dryed pepper flakes and thyme; saute over medium heat for about 5 minutes.
Add in sherry; simmer for 2 minutes.
Transfer the mixture to a small bowl.
Season the chicken strips with seasoning salt and pepper.
Add in more oil if neded to the pot.
Add in the chicken, stirring until browned.
Add in 2 tablespoons flour stir to coat the chicken evenly.
Add in the chicken broth with the onion/mushroom mixture; bring to a boil, stirring with a wooden spoon; simmer for about 25 minutes (you can cook a little longer if desired).
After about 25 minutes, add in the spinach chopped spinach, whipping cream, mustard and paprika (if using); simmer for about 5 minutes (at this point you can add in about 1/4 cup Parmesan cheese if desired) then season with salt and pepper.
Sprinkle with more grated Parmesan cheese, or pass the cheese at the table.