Prepare the marinade by combining lemon juice, lemon zest, olive oil, Dijon mustard, chopped parsley, minced garlic, Kosher salt, and black pepper in a small bowl. Whisk until well mixed.

Trim the silvery skin from the pork tenderloin to help the marinade penetrate the meat.

Place the tenderloin in a sealable container or zip-top bag and pour the marinade over the pork, ensuring it is evenly coated. Seal tightly and allow to marinate at room temperature for at least 30 minutes, or overnight in the refrigerator for best results.

Preheat your oven to 425°F (220°C).

Heat a large cast iron skillet over medium-high heat and add a tablespoon of olive oil.

Sear the marinated pork tenderloins in the skillet for about 2 minutes on each side until nicely browned.

Transfer the skillet directly to the preheated oven and bake uncovered for approximately 18 minutes, or until the internal temperature reaches 145-160°F.

Once done, remove from the oven and loosely cover with aluminum foil. Let the pork rest for 5-10 minutes before slicing.

Slice the pork into medallions about 1/2-inch thick and serve.