Preheat oven to 400 degrees

Squeeze any excess moisture from the spinach. Combine spinach, feta, red pepper flakes, and 2 T of olive oil in a small bowl.

Lay the pork loin on a flat work surface. Generously season the inside with salt and pepper. Line with prosciutto and top with spinach mixture. Roll up the loin and tie with kitchen twine at 1/2 inch intervals.

Heat the remaining tablespoon of olive oil in a large, oven proof skillet. Add the loin and cook until browned on all sides, about 10 minutes.

Add chicken stock and scrape the pan to remove any browned bits. Transfer the skillet to the oven and roast for 40-45 minutes until the internal temperature reaches 145 degrees.

Remove from the oven and allow to rest, covered in foil, for 15 minutes before slicing