In a bowl, whisk together the olive oil, soy sauce, vinegar, lemon juice, Worcestershire sauce, parsley, dry mustard, pepper, and garlic. Set aside 3 Tbsp of the marinade in the fridge for later when making the pan sauce.
Pour the rest of the marinade into a gallon sized Ziploc bag. Place the tenderloin in the marinade. Seal the bag and refrigerate for 3-4 hours.
Preheat oven to 350 degrees.
Heat an oven safe skillet over medium heat, remove the tenderloin from the marinade and sear each side in the skillet. This will take a couple of minutes per side.
Then place the oven safe skillet in the 350 degree oven and bake the tenderloin for 30-40 minutes until it is 160 degrees. Remove from the pan to a platter to rest for 5 minutes.
While it rests. add the chicken broth to the skillet over medium heat on the stove top to deglaze the pan. loosening up all the goodness left from the roast in the pan.
Then add in the reserve 3 Tbsp of marinade and bring the mixture to a boil. Let it boil to reduce for about 2-3 minutes. Remove from the heat and mix in the butter.
Slice the pork tenderloin into medallions and pour the pan sauce over the slices to serve.