Prepare the beef roast by rinsing it under cold water, patting it dry, and cutting a pocket into it for stuffing.
Make the stuffing by sautéing spinach and mushrooms in olive oil, then mixing with breadcrumbs, cheese, parsley, thyme, and rosemary.
Stuff the beef roast with the prepared stuffing, pressing it in firmly.
Tie the roast securely with kitchen twine and season the outside with salt, pepper, garlic powder, and onion powder.
Cook the roast in a preheated oven at 350°F for 1.5 to 2 hours, until the internal temperature reaches 135°F for medium-rare.
Let the roast rest for 10-15 minutes before slicing to allow juices to redistribute.