Preheat the oven to 400 degrees F. Spray a 9X13-inch baking dish with cooking spray.
Slice the pork tenderloin across horizontally but not in half, leaving one side attached (for easy stuffing).
Place the pork tenderloin in a Ziplock bag and seal it. Pound with a meat tenderizer or rolling pin until thicker parts are even to thinner parts. Remove from bag and place the prepared tenderloin on the prepared baking dish.
In a medium bowl combine the cream cheese, spinach, garlic, basil, parsley, salt, and black pepper. Mix well until combined.
Open the tenderloin and stuff it with the cream cheese and chopped spinach mixture. If it is hard to handle you can tie the pork tenderloin together with butchers twine.
Bake in the preheated oven for 27-30 minutes, or until the internal temperature of the pork reaches 140 degrees Fahrenheit. The internal temperature will continue to rise 5 to 10 degrees after you remove the meat from the heat, so it is important not to overcook the meat. It is safe to eat once it reaches 145 degrees Fahrenheit, so check the temperature after it sets for a few minutes, covered. Garnish with fresh basil leaves and salt and pepper to taste. Optional to also drizzle with olive oil before serving. Serve right away.