Prepare the beef tenderloin by trimming excess fat and tying it into a uniform shape.
Heat olive oil in a skillet and sauté garlic, mushrooms, and spinach until softened.
Stir in the cream cheese, breadcrumbs, thyme, salt, and pepper into the sautéed mixture.
Allow the stuffing to cool before filling the beef tenderloin.
Stuff the tenderloin with the mixture, securing it with butcher twine.
Sear the stuffed beef tenderloin on all sides in the skillet.
Transfer the seared tenderloin to a preheated oven and roast until the desired doneness is reached.
Remove the beef from the oven and let it rest before slicing.
