Remove the Silver Skin from Pork Tenderloin: Hold your knife at a slight angle under the layer of white skin and guide it along the outer edge of the tenderloin without removing too much of the meat.

Butterfly the Pork Tenderloin: Estimate where the halfway mark is in terms of thickness then cut into the meat lengthwise, stopping before you slice all the way through it. When you flip it open, it should have two matching sides, resembling a butterfly or an open book.

Pound the Pork Tenderloin: Place the opened piece of meat between two pieces of plastic wrap. Using the flat end of a meat mallet, pound the tenderloin until it is about 1/2-inch thick uniformly. Keep covered with plastic wrap and set aside.

Preheat oven to 400°F.

Prepare the Stuffing: Place a large oven-safe skillet over medium heat. Add 2 tablespoons of the olive oil with the chopped bacon. Cook until browned for about 3 go 4 minutes. Add the mushrooms and chopped onion; sauté for about 5 minutes or until soft. Add the minced garlic along with the chopped fresh herbs. Season with 1/2 teaspoon of salt & 1/4 teaspoon black pepper. Cook for one more minute, stirring constantly. Transfer to a plate. 

Stuff the Pork Tenderloin: Spread the mushroom mixture evenly over the surface of the meat, leaving about a 1/2-inch border all around. Starting with a long end, roll tightly like you would with a jelly-roll. Where the edge of the tenderloin meets up with the rolled meat, secure it with five or six toothpicks. Place them diagonally in a row, keeping in mind that you need a flat surface for searing the meat in the skillet. Season all over with the remaining teaspoon of salt and 1/4 teaspoon of black pepper. 

Cook the Stuffed Pork Tenderloin: Heat the same skillet over medium heat and add the remaining 2 tablespoons of olive oil. Once the oil is hot, place the tenderloin in the skillet (toothpick-side-down) and sear for about 2 minutes per side for a total of 6 to 8 minutes in all. Transfer the skillet with the tenderloin to the oven and bake at 400˚F for 18 to 20 minutes or until an instant read thermometer registers at 145°F in the thickest portion of the meat.

Let it rest: Transfer to a cutting board, brush with the pan drippings and rest for about 10 minutes before slicing into rings. Brush with any additional pan drippings for more flavor and garnish with parsley, if desired.