Preheat oven to 350 degrees. Mix drained green beans in a medium bowl. Add small can of sliced mushrooms, half of french fried onions, alfredo sauce and evaporated milk and stir well. Place in 9 by 9 greased baking dish. Bake for 35 minutes or until bubbly. Top with remaining onion rings during last 10 minutes of baking. Let stand 10 minutes before serving.