In a large skillet, brown hamburger patties on medium high heat. Remove from pan. Drain off excess grease if any.
Into skillet, french onion and cream of mushroom soup. Stir until well blended. Place browned hamburger patties into gravy mix. Top with mushrooms. Cover with lid and simmer for 30 minutes on low heat.
Add salt or pepper to taste. I do not recommend adding any salt (this is well-salted as is).