Begin by cutting the tenderloin into thick medallions.
Sprinkle salt on both sides of the medallions to season them.
In a small bowl, prepare the spice rub by mixing flour, chili powder, garlic powder, onion powder, smoked paprika, and 1/2 teaspoon of black pepper.
Pat the pork medallions dry with a paper towel and rub both sides with the spice mixture.
Heat oil in a skillet (with a lid) over medium-high heat until it becomes hot and shimmery.
Add the seasoned pork to the skillet and cook until it turns golden, approximately 2 to 3 minutes.
Flip the pork, so the seared side is facing up.
Reduce the heat to low, cover the skillet with a lid, and cook the medallions for 6 to 12 minutes, depending on their thickness. Check for doneness at 5 minutes, then check every 2 minutes thereafter.
Transfer the cooked pork to a plate and loosely cover it with aluminum foil. Let the pork rest for 5 minutes.
While the pork rests, prepare the pan sauce. Increase the heat to medium-high and add chicken stock, vinegar, and honey to the skillet. Use a wooden spoon to scrape up any stuck bits of pork from the bottom of the pan.
Let the sauce simmer until it is reduced by half. Taste the sauce and adjust the seasoning with more salt, vinegar, or honey if needed.
Slide the skillet off the heat, and when the sauce is no longer simmering, swirl in the butter.
Place the pork medallions back into the pan and spoon some of the sauce on top.
Sprinkle fresh parsley over the pork and serve.