Preheat your oven to 425°F (220°C).

In a large mixing bowl, combine fresh breadcrumbs, minced garlic, diced onion, melted butter, and chopped parsley. Mix until everything is well incorporated.

Take your beef tenderloin and place it on a clean cutting board. Carefully slice it lengthwise to create a pinwheel shape, then gently pound it flat.

Spread the prepared stuffing mixture evenly over the surface of the unrolled beef tenderloin.

Starting from one end, carefully roll the tenderloin up with the stuffing inside. Secure with butcher's twine at 1-inch intervals.

Generously season the outside of the rolled tenderloin with salt and pepper.

Place the secured tenderloin in a roasting pan set on a wire rack. Roast for about 50-70 minutes, or until the internal temperature reaches 135°F for medium-rare.

Once done roasting, remove the tenderloin from the oven and cover it loosely with aluminum foil. Let it rest for 15-20 minutes.

After resting, carefully slice the tenderloin into thick rounds that reveal the colorful stuffing inside.