Preheat oven to 325 degrees.
Cut deep "pockets" ¾-inch apart into the tenderloin, making sure not to slice through the roast. Set aside.
Sauté onion in olive oil for about 5 minutes.
Add mushrooms, wine and herbs. Sauté 10 more minutes, until most of the liquid is absorbed.
Add spinach, beans, almonds and cheese. Spoon this filling into tenderloin "pockets."
Place stuffed tenderloin in a lightly oiled roasting pan, and bake for 2 to 3 hours, or until internal meat temperature reaches 170 degrees.
Cool for 15 minutes before slicing.
Cover tenderloin loosely with foil after 45 minutes in oven to retain moisture and prevent over-browning.