Blend marinade ingredients in a zip-lock bag and add tenderloin. Seal bag and marinate overnight. Remove meat from bag and discard marinate. With a long, sharp knife, cut a slit into and down the length of the tenderloin to create a pocket to stuff.

Heat olive oil in pan; add spinach and sauté for 1 minute. Add breadcrumbs and garlic. Toss together well. Remove from heat, and allow to cool slightly. Stuff tenderloin with stuffing and wrap with string to seal.

Place in a lightly greased shallow baking dish. Bake at 350 degrees for about 1 to 1-1/2 hours for desired doneness. Remove string and cut into 1/2 inch slices to serve.