Preheat the oven to 350 degrees.
In a bowl, mix together the sour cream, ¼ cup of the Parmesan cheese, xanthan gum, Italian seasoning, garlic powder and salt and pepper to taste until well combined.
Place the tenderloins in a well greased baking dish.
Spread the sour cream mixture over them.
Sprinkle the mozzarella cheese and remaining Parmesan cheese on top.
Bake for 40 minutes.
Sprinkle with chopped parsley before serving.