Heat oil; add onion and cook until golden. Add meat and cook until meat loses its red color, stirring. Add mushroom sauce and salt, heat. Arrange in casserole half of noodles, half of sauce and half of cheese; sprinkle with seasoning salt. Make another layer of noodles; add sauce and top with cheese. Bake in preheated moderate oven (325°F.) for 1 hour. Top should be nicely browned. Makes 8 – 10 generous servings.