Preheat the oven to 400°F and line a baking sheet with aluminum foil. Set it aside.

In a medium bowl, combine garlic powder, salt, pepper, dried parsley, and onion powder. Whisk to combine.

Pat pork tenderloin dry with paper towels. Sprinkle seasoning mixture on all sides, and on the ends of the pork. Rub into the pork with your fingers to evenly distribute seasonings.

In a large skillet over medium heat, add olive oil. Once olive oil is hot and shimmering, add the pork tenderloin and sear the pork until browned on all sides. Once browned on all sides and ends, remove from the skillet and place on the aluminum foil.

Place 3 squares of butter evenly spaced on top of the pork tenderloin and wrap aluminum foil tightly around the sides, top, and edges.

Place in the oven and let roast for 20 to 30 minutes, or until the internal temperature reaches between 145 to 160°F in the middle of the tenderloin when tested with a meat thermometer.

When the pork tenderloin reaches the desired temperature, remove it from the oven, sprinkle fresh parsley over the top, and tent with aluminum foil.

Allow meat to rest for 5 minutes before slicing against the grain to serve.