Untie roast and set aside. For stuffing, in skillet cook mushrooms, onion and red pepper in hot oil till onion is tender. Stir in remaining ingredients. Spread stuffing over one loin to within one inch of edges. Top with remaining loin. Tie securely with string. Place roast in shallow roasting pan.
Roast in a 350 degree F. oven for 1 1/4-1 1/2 hours, until internal temperature on a thermometer reads 145 degrees F. Remove roast from oven; let rest about 10 minutes before slicing to serve.