Preheat the oven to 400 degrees.
Place the pork tenderloin on a cutting board. Trim any fat from the meat then remove the silverskin (click here for instructions). Using a very sharp knife make a lengthwise cut down the center of the pork tenderloin, cutting to but not through the other side. Spread the meat open and place a piece of plastic wrap over the top. Working from the center to the edges, pound lightly with the flat side of a meat mallet to form a rectangle.
Stir together chopped spinach, mushrooms, roasted bell pepper, basil, panko crumbs, minced garlic, and Parmesan cheese in a bowl. Season the pork tenderloin with sea salt and freshly cracked pepper, to taste then spread the spinach mixture evenly over the pork. Roll up jelly-roll style. Use toothpicks to seal together. Season the pork with sea salt and freshly cracked pepper, to taste.
Heat the olive oil in an OVEN PROOF skillet over medium high heat. Place the stuffed pork tenderloin in the pan and cook for 4-5 minutes or until golden brown. Flip the pork over and place into the oven for 25-30 minutes or until the pork reaches an internal temperature of 160 degrees. Remove from the oven and let the meat rest for at least 5 minutes before slicing and serving. Enjoy.