Instructions

1. Preheat your oven to 425F.
2. In a small nonstick skillet coated with cooking spray, saute the mushrooms until they're tender. Add the garlic and cook for 1 minute.
3. In a small bowl, combine the mushroom mixture, spinach, and cheese, then set aside.
4. Cut a lengthwise slit down the center of the tenderloin to within 1/2 inch of the bottom.
5. Open the tenderloin so it lies flat and cover it with plastic wrap.
6. Flatten it to 3/4 inch thickness. Remove the plastic and sprinkle it with 1/2 teaspoon salt and 1/4 teaspoon pepper.
7. Spread the stuffing mixture over the meat to within 1 inch of the edges.
8. Wrap up the tenderloin (the best you can) and tie it at 2 inch intervals with kitchen string.
9. Place it on a rack in a shallow roasting pan and sprinkle it with the remaining salt and pepper.
10. Bake, uncovered, at 425F for 30 minutes or until the meat reaches your desired doneness (for medium-rare, a meat thermometer should read 145F; medium, 160F; well-done, 170F).
11. Let it stand for 5-10 minutes before slicing.