Melt the butter in a 12-inch skillet over medium low heat. Add in garlic, onions, and red pepper flakes. Sauté for 30 seconds to coat the onions with the garlicky butter.
Add mushrooms, chicken, spinach, tomatoes, Italian seasoning, salt and pepper and stir well.
Pour in heavy whipping cream and mix. Cover the pan and cook for 15 minutes, until the chicken has cooked through.