Preheat your oven to 375°F (190°C). Pat the beef loin dry with paper towels.
In a small bowl, combine olive oil, Dijon mustard, garlic, rosemary, thyme, salt, pepper, paprika, and onion powder if using. Rub this mixture all over the beef loin.
Heat a large oven-safe skillet or roasting pan over medium-high heat. Add a little oil once hot and sear the beef on all sides until golden brown.
Transfer the pan to the oven and pour in chicken broth or water around it. Roast uncovered for about 50–70 minutes or until the internal temperature hits 140–145°F (60–63°C).
Remove the roast from the oven and tent it with foil to keep warm as it rests for at least 10–15 minutes before slicing.
Slice into thick medallions after resting and serve with your favorite sides.