Preheat your oven to 425°F (218°C).
Mince the garlic cloves and finely chop the fresh rosemary and thyme.
In a small bowl, combine the minced garlic, rosemary, thyme, sea salt, and black pepper.
Pat the beef tenderloin dry with a paper towel and rub with 0.25 tbsp of olive oil, then coat all sides evenly with the garlic-herb mixture.
Heat a cast-iron skillet over medium-high heat and sear the beef on all sides until a golden-brown crust forms, about 2 minutes per side.
Transfer the skillet to the oven and roast for 15-20 minutes, or until the internal temperature reaches your desired doneness (135°F for medium-rare).
While the beef roasts, heat the remaining 0.25 tbsp of olive oil in a separate pan over medium heat and sauté the asparagus and sliced mushrooms until tender and slightly charred.
Remove the beef from the oven and let it rest on a cutting board for at least 10 minutes before slicing to keep the meat juicy.
Slice the beef into medallions and serve immediately alongside the sautéed vegetables.