Pat the pork tenderloin dry with paper towels and season it all over with salt, black pepper, garlic powder, and onion powder.
In a large oven-safe skillet, heat the olive oil over medium-high heat. Once hot, add the pork tenderloin and sear for about 3-4 minutes on each side until browned.
Transfer the skillet to the preheated oven and roast the pork for 20-25 minutes, or until the internal temperature reaches 145°F.
Remove the skillet from the oven and transfer the pork to a cutting board. Cover it loosely with foil and let it rest for 5-10 minutes.
While the pork is resting, prepare the sauce in the same skillet. Over medium heat, add the heavy cream, Dijon mustard, thyme, and lemon juice. Stir to combine and let it simmer for about 5 minutes until slightly thickened.
Slice the pork tenderloin into medallions and serve drizzled with the creamy Dijon sauce. Garnish with chopped parsley.
Notes
For a lighter version, substitute half of the heavy cream with low-fat yogurt.
You can also add sautéed mushrooms or spinach to the sauce for extra flavor and nutrition.