Make the pork marinade by combining the oil, soy sauce, vinegar, lemon juice, Worcestershire sauce, fresh parsley, garlic, dried mustard, sea salt, and freshly cracked black pepper to taste in a large zip-lock bag. Add the pork tenderloin and seal; refrigerate for at least 4 hours.
Preheat the oven to 350 degrees.
Sear the pork tenderloin by heating the olive oil in a large cast-iron skillet over medium-high heat. Remove the pork from the marinade and sear each side of the meat for 4-5 minutes. Side Note: Reserve 3 tablespoons of the marinade for when making the pan sauce.
Roast in the oven for 18-20 minutes or until the internal temperature reaches 145 degrees with a meat thermometer.
Let rest loosely covered with a foil tent.
Meanwhile, prepare the pan sauce by placing the cast-iron skillet back on the stove over medium heat.
Add the chicken broth, scraping up all the browned pieces from the bottom of the pan.
Add the reserved marinade and let it boil down for 2-3 minutes.
Add the butter and fresh parsley. Remove from heat, stirring until butter has melted. Taste the sauce and re-season if needed.
Slice the pork tenderloin and serve it with the sauce drizzled over it. Enjoy.