Preheat oven to 325°F. Cover a cookie sheet with foil. Spread Cheez Whiz on bread halves, place on cookie sheet.
Brown ground beef in a skillet. Pour off excess fat. Add peppers. Add 1/2 can of tomato sauce, heat to boiling. Simmer 5 min, add oregano & salt to taste. Cook 2 min longer. Spread meat mixture on both bread halves. Top with onions and mushrooms. Spoon a little tomato sauce over all. Drizzle oil to keep from drying out. Top with cheese.