Preheat oven to 350 degrees F (175 degrees C). Lightly grease a9x5 inch loaf pan.Heat the olive oil in a large skillet over medium heat. Stir in themushrooms, onions, and bell pepper; cook until the onion istransparent, about 5 minutes. Sprinkle sage over the vegetables,and cook until vegetables are soft, about 5 minutes more. Transfervegetables to a large mixing bowl.Stir the rice, walnuts, onion soup mix, oat bran, wheat germ, eggwhites, Worcestershire sauce, and mustard into the mushroommixture until thoroughly blended. Spoon into prepared loaf pan,pressing down mixture with a spatula to flatten top.Bake in preheated oven for 1 hour. Let rest 10 minutes beforeslicing.