Using a meat mallet (or rolling pin or heavy skillet), flatten each piece of tenderloin to 1/2". thin even pieces.
Sprinkle surfaces of pork with lemon pepper, then your choice of flour...this really just a sprinkling to gave it added crunch, but you could forgo the flour altogether if you'd like: I just like the texture it provides!
Heat ghee or butter in heavy cast iron skillet over medium heat; brown pork evenly, about 3 minutes on each side. I like to wait and flip the them when I see the cooked pork color creeping up the sides of the piece.
Remove to serving platter, keep warm, turn heat to low.
To the pan, add lemon juice, Worcestershire sauce and mustard to skillet. Cook, stirring with pan juices, until heated through. Pour sauce over medallions, sprinkle with parsley and serve.