Preheat oven to 400 degrees F. Split tenderloin open down its entire length. Season generously inside and out. Spread spinach to cover inside surface. Top with roasted peppers and garlic. Sprinkle with Parmesan. Reform tenderloin and tie every 3 inches with butchers twine, to hold in the filling. In a large saute pan heat oil and sear meat on all sides. Roast on a rack in a roasting pan for 15 to 20 minutes or until a meat thermometer registers 120 to 125 degrees F for rare (for medium-rare, roast until temperature registers 135 to 140 degrees F). Remove, cool completely and wrap air tight for your picnic.